irin,
i think it also depends on whether the people around them 'spoil' them or not.. some people always have others to help them.. usually parents/siblings etc.. so if they have a lot of such help, they don't feel the pressing need to 'grow up'.
i have this temp staff last time.. she shotgun.. then married the boyfriend.. i saw her hb's pic, i want to faint.. cos he looks just like a boy.. the "boy" holding the real boy (baby)..
well, the guy is still in the army! i think 19yrs old.. the girl, altho they got married, but weekdays she stay at home with her parents (and her baby).. weekend then she go over to her hb's place.. she is still planning to go for further studies (private institute).. and her parents are paying for her studies! and meanwhile now, her parents are paying for her baby's milk powder, diaper etc.. i think the guy also got give money la, but NS pay... like few hundred bucks! oh well..