It's not that big of a difference. It's like this: if (God forbid) you get injured by a hit and run driver, it doesn't matter what make of car they were driving. What matters is that you got injured.

The human brain does not become fully mature until the mid 20's. The last part to become mature is the frontal lobes, which govern foresight and principled morality. An adult who sexually abuses a teenager is no different from someone who sexually abuses a person who is asleep or otherwise incapacitated.