I think there is a difference between:

The age gap if you both really love each other for who they are, and you aren't loving them just for the fact they are younger and the attributes that come with it. The younger memeber must also realize fully the responsibility of a relationship.

vs

A person who just loves the idea dating of a young kid for the way they look and act (the whole innocence thing) and taking advantage of the fact that a person at that age does not know any better; since they are not mature enough.

I actually think they should be off limit till they fully understand the rights and wrong, and know what they are getting themselves into. If you plan to date someone much younger than you, you have the responsibility of informing them that and making them decide that is assuming they are old enough to decide.