There is no universally agreed upon age when a child legally becomes an adult. Different countries, cultures, societies, and even individuals have varying perspectives on when a person should be considered an adult versus a child. However, there are some common milestones and considerations that can help provide a general framework for understanding when a person transitions from childhood into adulthood.
The legal perspective
Legally, the age at which a child becomes an adult varies significantly across different countries and jurisdictions. Some of the most common ages that mark this legal transition are:
| Age 16 | United Kingdom, Canada (except Quebec), Australia, New Zealand |
| Age 17 | Quebec |
| Age 18 | Most U.S. states, India, Philippines, Indonesia, Egypt |
| Age 19 | Korea, Taiwan |
| Age 20 | Japan, Iceland, Norway |
| Age 21 | Singapore, Hong Kong |
At these ages, a child legally becomes an adult, obtaining all the rights and responsibilities of adulthood. This includes the ability to vote, consent to medical treatment, enter legal contracts, join the military, marry without parental consent, be tried as an adult in court, purchase alcohol, and more.
Of course, not all rights and privileges are granted at the same age. For example, in the U.S. the ages for purchasing alcohol (21), military enlistment (18), and voting (18) all differ. So the legal transition to adulthood can be gradual.
Physical and sexual maturation
Biologically, puberty is the process of physical change that leads to sexual maturity and the potential to reproduce. The ages that mark the end of puberty and sexual maturation into adulthood are much more variable than legal ages of adulthood, for several reasons:
- The timing and stages of puberty vary significantly between individuals based on genetics, nutrition, environmental factors, and more.
- Puberty onset occurs at different average ages in different populations. For example, the average age of first menstruation for girls in the U.S. is around 12-13 years old, versus 15-16 years old in India.
- There are individual differences in when full sexual maturation is complete after the initial onset of puberty.
However, we can make some broad generalizations about common ages that mark different stages of puberty:
| Girls | Boys |
| First visible signs of puberty: 8-13 years old | First visible signs of puberty: 9-14 years old |
| Menstruation begins: 10-16 years old | Voice deepening begins: 12-15 years old |
| Reaching adult height: 10-16 years old | Reaching adult height: 12-18 years old |
So while the onset of puberty may begin around ages 8-14, full sexual maturation into adulthood is often not complete until the late teens or early 20s. This stands in contrast to legal definitions, where 18-21 is considered the entry to adulthood.
Brain development and maturity
Human brains are not fully developed until well into our 20s. Some of the last areas of the brain to mature include:
- Prefrontal cortex – Responsible for judgment, planning, problem solving
- Limbic system – Regulates emotions and impulses
- Neurotransmitter levels – Affects reward-seeking behaviors and risk taking
These parts of the brain are still developing during adolescence and into early adulthood. As a result, some experts argue that 18-21 year olds should not be considered fully mature adults due to ongoing neurological development.
Components of adult brain maturity include:
- Impulse control
- Long-term planning
- Regulation of intense emotions
- Delayed gratification and patience
- Consideration of long-term consequences
The incomplete development of these abilities in emerging adults is why some experts advocate that the brain is not truly adult until the mid-20s.
Financial and residential independence
Becoming financially independent from parents or caregivers is a major milestone towards adulthood. Supporting oneself financially signifies the ability to provide for one’s basic needs.
A few indicators of financial independence:
- Having a full-time job
- Paying for one’s housing
- Paying bills and living expenses independently
- No longer receiving financial support for necessities from parents/guardians
Similarly, moving out of one’s family home and living independently establishes residential self-sufficiency as an adult. Paying rent, managing a household budget, cleaning, cooking and home maintenance signify the skills needed for adult living.
In many modern cultures today, financial and residential independence do not occur until the early to mid-20s, suggesting this transition to adulthood is extending later than in past generations.
Completion of education
Finishing one’s education, whether that involves graduating high school, college, graduate school or vocational training, can mark a transition into adulthood.
Educational completion indicates certain abilities like:
- Following through on long-term commitments
- Self-discipline to meet deadlines and obligations
- Critical thinking and analysis skills
- Specialization of knowledge in a field
Today, with more students pursuing higher education past high school, graduation from a bachelor’s or graduate degree program in the early to mid-20s can signal an individual’s progression into adult roles and responsibilities.
Entry into the workforce
Gaining full-time employment is a major milestone of adulthood. Beginning a career signifies:
- Financial independence and self-sufficiency
- Practical real-world skills and experience
- Contributing productively to society
- Accountability to show up reliably and meet expectations
- Planfulness about one’s professional future
Starting a first substantial job often occurs in conjunction with other markers like finishing education, residential independence, and financial self-sufficiency. Entry into full-time work necessitates adopting adult responsibilities.
Marriage and children
Marriage and parenthood have long been seen as transitions into adulthood, with good reason. These major life events require:
- Commitment to family responsibilities
- Financial resources to support dependents
- Emotional maturity to care for others
- Patience and self-sacrifice in parenting
- Stability and wisdom to advise younger family members
Of course, not everyone follows the traditional path of marriage and children. But for those who do, these roles undeniably shape an adult identity and purpose.
Cultural and societal definitions
Ideas about when a child becomes an adult are also culturally determined. Different cultures and societies have their own perspectives on coming of age.
Some examples include:
- Bar/bat mitzvahs in Jewish culture (around age 13)
- Quinceañeras in Latin American culture (15th birthday)
- Sweet 16 parties in American culture (16th birthday)
- Debutante balls announcing a young woman’s entry into society (variable ages)
These cultural rituals symbolically recognize an individual’s transition into adulthood and acceptance of adult roles. The ages and definitions vary between cultures.
Conclusion
There is no universal biological, legal, or cultural agreement on when a child becomes an adult. It depends significantly on societal norms and individual circumstances. However, common thresholds include:
- Legal definitions: 18-21 years old
- Physical development: Late teens to early 20s
- Brain development: Early to mid-20s
- Financial independence: Early to mid-20s
- Completing education: Early to mid-20s
- Full-time work: Early to mid-20s
- Marriage/children: Variable by individual
- Cultural rituals: Variable ages per culture
While the journey to adulthood is gradual, most individuals today are likely not considered fully adult until at least 18 years old, if not older. But exceptions certainly exist in both directions, as individual maturity varies substantially.
