People who have just reached puberty are far easier to manipulate into having sex than someone who's older. I think the point of the law is to stop older men from using children as something like a prostitue; Instead of money, give them a lolipop and attention, get laid. The point of the age limit is that if you haven't learned not to get into that kind of relationship by the time you're 18, you're not going to learn.

I don't think there's necessarily anything immoral about a relationship with a large age difference, but I think it is more likely to be than the "normal" relationship.

My state has an exemption from age of consent if the people involved are over 14 and less than three years apart in age. I think 5 would be more fair. I think the real problem with consent laws is that so many of the people reporting the "crime" are parents who doesn't like who their child is dating.