To the 13 year old.
Your 17 year old boyfriend is the one with the big problem.
While at 13 years, for a girl, sex can be put on hold or slowed down,
for a 17 year old guy, his sex drive is going full speed ahead.
His body will immediately react to even seeing you and to every sexual thought. It is a very powerful situation for you to have a older guy take an interest. However, this is very frustrating and conflicting situation for him.
It is very rare for a young guy to be able to completely control him self
and not take advantage of a younger less experianced partner.
If your boyfriend is very restrained, self controlled and idealistic, you might stand a chance.
If he is communicative and not manipulative, you might want to work out some ground rules.