The idea of legal adulthood is extremely interesting to me, because there are so many variations in personal emotional and social development. However, the legal ages laws in different "westernized" countries are as follows:
Australia: 10- criminal responsibility, 16/18- legal adulthood (depending on the area)
Canada: 18/19- legal adulthood (depending on the area)
UK: 10/12- criminal responsibility, 18- legal adulthood, 21- adoption, personal license holder, etc.
US: 18- legal adulthood, 14 through 18- adult criminal responsibility (depending on area), 21- alcohol possession and consumption.
The legal age of consent varies considerably throughout all of the world.