Well, then your family has a screwed up idea of what 'growing up' means. Most people don't equate 'marriage' with 'adulthood.' Getting married/becoming a parent doesn't make you an adult. There are plenty of example of people in bad marriages or people that abuse their children because they aren't 'grown up.'
Not to bash your family, but I almost feel sorry for their spouses/children if the only reason they got married (or started a family) was to prove that they were 'more adult.'
That's almost as bad as those 14 year old girls that have sex with 30 year old guys and are purposefully trying to get pregnant (as in doing things like puncturing condoms). They are just trying to prove that they are 'adult' and 'mature,' but they really will end up being the trashy horrible mom because they weren't ready to be a mother at all yet (if they ever would have been otherwise).