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In most countries, there is the concept of adulthood, which brings with it several rights and responsibilities. In many countries like the Commonwealth nations, it is 18. Is there any scientific basis to choosing that particular age?

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In Canada, we have some provinces that use 18, and others that use 19, which results in the strange situation where you can drive to another province and make decision that are illegal in the same country, in your home province. – Nthaoe Apr 11 '11 at 12:45
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Where I live, various "adult" activities are allowed at 15, 16, 18, or 21. The severity of consequences from those activities really don't seem to have much relation to the age either. At first glance it appears to be purely political rather than scientific in basis. – Brian Knoblauch Apr 11 '11 at 13:07
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The 'Age of Majority' has changed throughout history. Wikipedia has a list of countries and their current age of majority – Oliver_C Apr 11 '11 at 13:09
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I would hazard a guess that it's because that's when most people finish secondary school. When Ontario raised the drinking age from 18 to 19, it was to keep alcohol out of the high schools. (Ontario had an extra year of high school then.) – Chris Cudmore Apr 11 '11 at 17:30
At what age were humans evolved to be considered as "adult". I'd argue that it's as soon as the females can reproduce. After that, it's a decision of society, at what point do we feel comfortable allowing these people to decide our future? (vote) – Nthaoe May 25 '11 at 1:36
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closed as not a real question by Larian LeQuella♦ Apr 7 at 12:47

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

5 Answers

up vote 24 down vote accepted

(I note with a wry smile that you asked for scientific basis while giving it a "Law" tag. While not mutually exclusive, laws are made by politicians and legislators, and rarely linked to science.)

Before citing a scientist on brain development maturity, have you ever noticed that many jurisdictions will let you drive at age 16, while rental car agencies will seldom rent cars to those of that age?

(Think about what goes into renting a car: credit cards, trip planning, and decision making, to name a few. And what goes into driving itself: impulse control, attention, and more decision making. Now think about handing your keys over to a sixteen-year-old versus a twenty-five-year-old.)

Much brain research has described the integration of the prefrontal cortex with the rest of the brain. The integration does not usually finish until 10 years after puberty, or around 25 years of age. (The human frontal lobes: functions and disorders by Bruce L. Miller and Jeffrey L. Cummings, p. 577)

They cite Joaquin Fuster (2002):

The DPFC is responsible for inhibiting impulses, weighing consequences of decisions, and most importantly, prioritizing and strategizing to obtain a solution to the presenting problem.

(DPFC is an abbreviation for Dorsal PreFrontal Cortex.)

I do not think there is a scientific basis for how governing bodies set the age of adulthood. Is a person endowed with a certain wisdom on his 18th or 21st birthday? You probably know of 30-year-olds who should not been endowed with the rights to sign contracts, to marry, to drink alcohol, to drive, to drink-and-drive, and so on.

The de jure standard seems to be a tradeoff between giving young persons responsibilities and rights and protecting the rest of society from the exercising of those rights.

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Agreed. I also know of 14-year olds who should have been endowed with all those rights; we have to draw the line somewhere. – Tortoise Nov 4 '12 at 17:05
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It is a totally arbitrary distinction made for economic reasons. In most western countries, secondary education is complete by the time someone reaches the age of 18, and thus are considered a member of the workforce.

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Nothing in that link supports your assertion that it’s “totally arbitrary”. Your second sentence is idle speculation, and I believe it’s wrong since it’s confusing correlation with causation. How come this answer is upvoted so much? – Konrad Rudolph♦ Apr 12 '11 at 12:19
@Konrad - Nice point about the causality vs. correlation. Somebody somewhere said about the age being reduced from 21, so there may in fact be a causality there. – apoorv020 Apr 12 '11 at 17:57
up vote 4 down vote

First of all, here is a link to 2 people's answers, which enlightened me on the matter.

As far as I know, the age of 18 has been chosen in many countries just as an average of ages on which people showed a mature behavior. It's an age at which many people are fully grown, have a free choice of education, and are enough life-experienced to be an independent being (ie don't need the protective arms of the parents).

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up vote 3 down vote

This question is based on a false premise.

In most countries, there is the concept of adulthood, which brings with it several rights and responsibilities. In many countries like the Commonwealth nations, it is 18.

That is a big over-simplification. There is not a single age at which children are considered adults, even in Commonwealth countries.

Consider, for example, the age at which you are:

  • Allowed to drive. 14-18
  • Allowed to consent to heterosexual sex 12-21 Note: Ages of consent for homosexual and anal intercourse are at a higher age in some jurisdictions than heterosexual and vaginal intercourse.
  • Allowed to consent to marriage. 15-22
  • Allowed to purchase cigarettes. 15-21
  • Allowed to vote. 16-21
  • Allowed to run for public office. (Some countries have higher age. You must be 35 to become US President.)
  • Allowed to enlist in the military. 17-22

It is clear that the choice of 18 years for some jurisdictions for some limits is a cultural, not scientific, decision.

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up vote 1 down vote

The UN convention defines childhood as goes up to 18: http://www.unicef.org/crc/index_30229.html

Why this is is perhaps the thrust of your question.

But that it is means that it would be very hard to shift the value from 18. It's locked into International Law and will persist until genetic engineering has created adults aged, say, six, that are required for military duty.

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Welcome to Skeptics. This seems to beg the question, as you point out in the second sentence. – Oddthinking♦ Apr 7 at 8:29

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