Pip is really cute! I like it on a boy.
I agree with the suggestions of
Peregrine and
Philo. I met a boy
Piper who's around 20, and I've liked it ever since, but I think that most people have trouble seeing it on a boy rather than a girl.
I think it could be a nickname for
Piran as well. Or maybe
Phoibos /
Phoebus?