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When Do Kids Become Adults

In parents’ eyes | According to the law | According to science | The change in social aspects of adulthood

In the United States, a child becomes an adult legally when they turn 18 years old.

However, “adults” can mean different things when you ask different people. Let’s find out what it means to become an adult according to parents, the law, and science.

When Do Kids Become Adults In Parents’ Eyes

For many parents, though, there’s always the question of “when do kids become adults?”

For some, a cursory internet search on state and local laws may suffice as an answer. For others, however, the idea that there is an age limit to childhood and a clean line in the sand for one’s entry into adulthood is a hard sell. 

Most parents anticipate their child’s transition into adulthood with a mix of emotions, including pride, hope, fear, and trepidation. And as time passes, many will say their roles and responsibility of adulthood are ever-changing. 

New parents will always be found standing close by, waiting patiently to catch their children when they fall. 

As kids continue on to adolescence, parents stand at the sidelines (literally and figuratively), guiding their child from a safe but comfortable distance. 

Eventually, the day will come when kids go off into the world to live their lives using all the life skills they’ve learned from their parents through the years. 

The truth is adulthood—true adulthood is far more nuanced than you might think.  

woman in graduation gown hugs father

When Do Kids Become Adults According To The Law

If we look through the eyes of the law for an answer, adult life starts when they are deemed competent enough to do certain things and participate in their society and government.

In the United States, the age of legal adulthood is 18 years old. However, young people can drive at 16 and join the military at 18. And they only reach the legal drinking and voting age upon their 21st birthday. 

Many would argue that there’s a terrible disconnect with some of these numbers. 

For example, an 18-year-old can join the military, but they don’t have the legal rights to vote for the government representatives who uphold The Constitution they’ve taken an oath to defend. Or, an 18-year old can go off to world war, but they cannot legally have a beer or a glass of wine. 

In Europe, including the United Kingdom, however, things are a bit different. While the age of majority is still 18 in most countries, young people can also drink at age 18, and for many countries, 18 is also the age when one can legally vote. 

Interestingly, in some countries, there are special circumstances where the age requirements are different for some individuals. 

For example, in Bosnia and Herzegovina, the legal age to vote is 18; however, if a young person is employed at 16, they can vote. Some may say that stands to reason. If you’re old enough to pay taxes, you should be old enough to have a say in the government that levies those taxes.

When Do Kids Become Adults According To Science 

While the law says one thing (at age 18 you’re legally considered an adult), science sheds some light on our brain’s inner workings to show us why adulthood is not a simple matter of age.

As children mature past late adolescence into early adulthood, significant changes in their brain anatomy and activity are still going on, and brain maturation continues far later into development been previously believed. 

This is especially true of the prefrontal cortex regions of the brain; the part of the brain that plays a large role in a variety of executive functions, including:

  • Attention and focus
  • Understanding and predicting the consequences of one’s actions
  • Impulse control
  • Emotional control
  • Future planning 
  • Comparing risk and reward

The prefrontal cortex of the brain is not fully developed until age 25​1​.

While neuroscience has given us answers about how the prefrontal cortex develops, how it functions when it’s fully developed, and how it affects us as individuals, the fact is there are individual differences in brain development​2​, and different regions of the brain develop at different rates​3​.

That means that some people will reach maturity before others. So blanket assumptions about what a person is and is not capable of have an inherent margin of error.

Some systems, like those for logical reasoning, often reach maturity by age 16; other systems, including self-regulation, are still developing well into young adulthood. 

So, while a 16-year-old may be deemed competent enough to make certain decisions, they may not be mature enough to make the best decisions or even to understand the consequences of those actions fully. 

Ultimately, the law recognizes and accounts for these differences as kids under a certain age cannot be tried as adults. (Age of criminal responsibility varies state by state.)

The Change in Social Aspects Of Adulthood

It used to be that a young person’s exit from high school and subsequent pursuit of higher education counted as a rite of passage into adulthood. 

For many families, kids graduating from secondary education and leaving their parents’ homes to become college students, and their eventual strides toward financial independence equaled adulthood as well. 

But times are changing, and the perception of adulthood is changing right along with it. 

In the absence of these usual rites of passage (that were socially accepted as such), sometimes kids and parents are at a loss to really define when kids officially become adults. 

Increasing Lack Of Autonomy

The perception of early adulthood is often deeply entwined with a feeling of autonomy, which certainly seems to be on the decline over the last few decades​4​.

While many parents may want a clear definition for when their kids become adults or they long for the day that the proverbial flip switches, their parenting style could have a profound effect on how and when that happens.

In today’s society, Overparenting, helicopter parenting, lawnmower parenting, or toxic parenting adopted by many baby boomers often present a direct challenge to that transition. 

The fact is if parents don’t give their children the opportunity to make their own decisions, the latitude to make and learn from their mistakes, and the space they need for proper development, it’ll be almost impossible for their children to understand what it truly means to be an adult​5​.

Usual Rites Of Passage Are Delayed Or Put Off Altogether

Three to four decades ago, the usual rites of passage for adult children were financial independence, marriage, having children, or buying a new home. 

But within the last few decades, these milestones are simply out of reach for many and being put off entirely for one reason or another. 

Without these benchmarks to concretely mark the transition, it’s more and more difficult for young people to think of themselves as adults, and it’s equally hard for their parents as well. 

It’s worth noting here, too, that if we only look at these rites of passage as the definitive markers of adulthood, the definition would still be all over the place. 

Things like race, ethnicity, gender, and social class also play a key role in the timing of these milestones.

Consequently, kids become adults at different times, depending on their cultural beliefs. 

Culture and religion

In many cases, culture and religion have their parameters for determining adulthood. Some cultural and religious recognitions of adulthood include: 

  • Bar or bat mitzvahs – Jewish observance of a child’s coming of age
  • Confirmations – Catholic observance of the transition from childhood to adulthood. (Although, it’s important to note that this is a recognition of adulthood only in the eyes of the church)
  • Quinceaneras – A coming of age ceremony (and party) typically observed by Mexican, Puerto Rican, Cuban, Central, and South American cultures.

It’s worth noting that while many of these long-held traditions are still observed and celebrated today, it’s primarily in name only, particularly in the Western world, where definitions of adulthood are often tempered by federal and state laws in local authorities.


  1. 1.
    Sharma S, Arain, Mathur, et al. Maturation of the adolescent brain. NDT. Published online April 2013:449. doi:10.2147/ndt.s39776
  2. 2.
    Foulkes L, Blakemore SJ. Studying individual differences in human adolescent brain development. Nat Neurosci. Published online February 5, 2018:315-323. doi:10.1038/s41593-018-0078-4
  3. 3.
    Mills KL, Goddings AL, Clasen LS, Giedd JN, Blakemore SJ. The Developmental Mismatch in Structural Brain Maturation during Adolescence. Dev Neurosci. Published online 2014:147-160. doi:10.1159/000362328
  4. 4.
    Twenge JM, Zhang L, Im C. It’s Beyond My Control: A Cross-Temporal Meta-Analysis of Increasing Externality in Locus of Control, 1960-2002. Pers Soc Psychol Rev. Published online August 2004:308-319. doi:10.1207/s15327957pspr0803_5
  5. 5.
    Locke JY, Campbell MA, Kavanagh D. Can a Parent Do Too Much for Their Child? An Examination By Parenting Professionals of the Concept of Overparenting. Aust j guid couns. Published online December 2012:249-265. doi:10.1017/jgc.2012.29

About Pamela Li

Pamela Li is a bestselling author. She is the Founder and Editor-in-Chief of Parenting For Brain. Her educational background is in Electrical Engineering (MS, Stanford University) and Business Management (MBA, Harvard University). Learn more


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