When I was freshman in HS my boyfriend was a senior in HS (i know it's not exactly the same as op friend's situation) and at the time I didn't think it was weird. It obviously wasn't legal during most of our relationship as I was with him 4 years or so. He aslo wan't very mature at all, which I think is the bottom line with most of these relationships that involve a very young person and someone who socially is looked at as being too old to be with them. If this guy acts like he is 14-15 it doesn't come as a surprise that he would go for a youngin. If he is just doing it to get some fresh putang that that's gross.
Even though I used to be in a similar situation, I who have to agree with most ofthe other replys - probably not ok