Is it wrong for a teenage girl to be in a relationship with a 30 year old man?

When my father and mother hooked up, my father was about 30 and my mother was about 16 at the time and became pregnant at 17. Today, over 36 years they are still together and they had a very successful marriage, but was it wrong for them to be together in the first place? Would you allow your 16,17 or 18 year old to be with a 30 year old guy, even if she claims that she is in love with him and the guy looks like a decent man? Now I know that it is against the law and all, but I am looking into the morality of the thing and the reasons behind such a law. If I were my mother’s parent I would not have allowed her to date him, but that is just me…what do you guys think?