Being a straight female, I don't know how much help I can provide. Personally, I think that age is a number, but obviously within a LOT of logical reason. Though it happens, it doesn't make much sense to me what someone in their twenties would want with someone who is say... fifteen. Though as you get older, I think age differences matter less and less, as that age, it almost seems silly - what's going to come of it? Probably not a serious relationship.
But, if both of you truly are in it just to get some, and you are thoroughly convinced that that's what you're looking for, then maybe it's not such a terrible thing - again, depending on what exactly the age difference is, and how safe you actually do feel. A lot of this is so dependent on the specific situation, for obvious reasons. But with your question the potential to be hurt emotionally, you hit on something really important. I think emotional attachment can come and bite you in the ass at really inopportune times, but it's such a personal thing. Some people can have involvement and simply turn off their emotions, and some people develop and keep emotional attachments. Granted, physical acts like what seem to be being implied here ARE inherently emotional, and I think they have to be handled carefully. Say you start out just wanting to "get a little," but you were to end up falling for this guy, though he was still just looking to get some. You could end up hurt. But, you could end up hurt in any relationship, I guess. I suppose that just because with an age difference over such a gap of maturity, being that one person in question is a teenager, with people in two very different stages of life, it might be much easier to get hurt.
Honestly, though, you need to do what you feel comfortable with.
A work of art is an invitation to love.