Well, only you can be the one to determine when you call him your boyfriend. That's totally your call.

I would tell you not to be nervous about being (so to speak) this guy if he has more experience than you, but don't let him pressure you, and don't jump into this before you're ready. The experience won't be a problem when that time comes, but you need to be sure that that time is something you both want.

As for how slow, personally if it were me (I'm not a woman, mind you, though I am about your age), I would want to be well in love with the person before I even considered a sexual aspect to the relationship, but to be fair, I am very "old fashioned" in regards to these things, and I can only offer my opinion on it. I would just tell you that if/when you decide to be with this guy, be sure you're comfortable with it, be sure it's not under a sense of "duty" to him or as a means to give him what you think he wants, and be sure it's safe.

I do hope others can offer their perspective on things, and I hope I was of some help. Good luck to you.