There are definitely regional differences as to when women are expected to be married and having children (and it seems to be mainly women who get the questions).
I'm from the Northeast US, and some people were very surprised when I got engaged at age 21. My dad actually told me, when I was 19 or so, that I wasn't allowed to date anyone until I had my doctorate.
(Like he could stop me!
) He felt I should be done with college and financially stable before thinking about marriage and kids. And - by our choice - we did wait until after we were done with college before getting married.
Of course, now that I'm in my late twenties and we've been married for a few years and are financially stable, my dad is all like "why aren't you pregnant yet?"