This discussion would never end. There is no magic number for maturity level, it varies from person to person and depends on many factors including but not limited to his environment, parental-teachings, education, company of friends etc.
A 14 years old can be mature enough to decide whether he/she want to have sex, drink or not .. or understand how to drive safely .. while a 19 years old chick can be dumb enough to get pregnant in a one-night stand etc.
