It sounds like you want us to talk you out of it. Otherwise, there would be no problem!
He may be mature, as most people are at that age, but there will be problems down the road. For example, if you plan on having children, there will be a good chance that they won't have a father for the majority of their lifetimes.
Your parents might be repulsed by the idea of you dating someone that could be their age. When both he and they grow old at the same time, you'll have a lot of responsibilities about caring for their health and seeing that their day-to-day needs are met.
You're not even old enough to drink, and this man is 2.5 times your age. Consider his motives and think carefully about your decision.
You say that he is very attracted to you, but what about you and why do you want to date him?
I dated a guy at that age once, it was difficult because at that age they are already developed strong views and personality and want the girl to admire them.
He probably has (had) family also, that's kinda tough to deal with...
Maybe you're lacking a father figure and are confused. Or he's offering you some type of security and that's what's attractive to you. Personally, I just don't see the appeal in it. Besides, when you're 30 and he's 60 you'll be spending your time changing his Depends.
Haha he would be george clooney....because otherwise I don't understand why a 20 year old would want a 50 year old