ragman makes a good point.
don't be flattered by the fact this "grown man" is paying attention to you.
Ask yourself why he is not trying to get girls closer to his age to go out with him?
I'm sure you're a very smart young lady, for you age. But I'm sure you can also see that there is a big difference between you and an 18, 19, 20 or 21 year old woman.
Not to insult you at all Mickey, but to most 20 year old guys, you are a kid. That's ok, because compared to them, you are.
Ask yourself why this guy wants to take the virginity of someone that all of his friends, co-workers, etc would think of as a kid?
Don't worry, you'll be 17, 18, 19 before you know it. When you are, you'll realize this guy should not have been bothering you when you were 13.
I don't understand why you'd want this person as a friend. He's trying to take advantage of you in a very bad way.