If his wish is to "see sex" rather than "watch porn", it should he possible to allow himbtobwatch movies or TV shows where sex can be seen. My own child ended up seeing "sex" at 11 because she watched Game of Thrones with me and my brothers one Christmas. She also saw a whole lot of violence, and it doesn't seem to have caused any form of trauma in her. Neither did it cause any greater interest in doing sex.
One movie recommendation I'd like to make is Love Actually. It's rather sweet, very British, and depicts several different types of relationships that are possible (with consent). It also shows how sex scenes in movies are a total scam, which may be good for discussing how porn is nothing but an act, with props like fake bodily fluids and everything. I don't expect a 13yo boy to like that movie, but at least it gives you something to talk about.
Another thing that may or may not be worth talking about is making out with girls. Many girls will give in to a boy, thinking that trying it won't cause any harm. And then if they find they didn't like it, they still won't say it. Almost as if they're afraid to hurt the boy's ego. So there are intimate situations that do not involve what we usually consider "sex" that still need consent. And taking a moment in the middle of it to ask if the other person still consents whole-heartedly, could be a rather wise decision. It's easy for youths to be caught up in the moment, forget to communicate with a partner, and thus they may not notice subtle signals that the other person is uncomfortable and possibly wants to withdraw their consent.
Slightly off topic, but I don't know where else I would mention it.