When does a child become a youth and in extension, when do a youth become an adult? Can anyone here clear this?

A child becomes a youth when he/she becomes a teenager......and i think teen starts from 13, while a teenager becomes an adult when hes above a teenage stage and i think that should be around 20.
However, some are more matured than their ages, therefore, its not uniform, a good parent is in d best way to know how well to handle individual child.
May God help us all.

Pls, where is your source for this info, is it a general standard'?

bilms: Pls, where is your source for this info, is it a general standard'?

its my personal opinion. Thanks.

Thanks