For a young man, that's not actually very premature.
In fact, statistically, it will take most women longer to orgasm, period (from ANY sexual activity) than it will men.
That's why considering only intercourse to be the whole of a sexual session is a faulty approach. And considering a great many women don't orgasm from just intercourse period, even more so.
So, rather than focusing on extending intercourse, why not wor on incorporating more recpetive sexual activities for you into your sexual life/sessions?