11/12 is on the younger side to become interested, but not abnormally so, in my opinion.
I remember having a keen interest in sex at around this age. Only one of my friends shared it, so when we had the chance we discussed it in depth (and those discussions were pretty weird, looking back on it now).
My daughter was the same - at around 11 she became very interested in sex, had strong crushes on certain celebrities etc. Her best friend is the same, and their discussions about it are pretty racy.
I have striven to keep an open, non-judgemental dialogue with her about this, answering her numerous questions in as honest a way as I can, while also keeping my answers age-appropriate. I acknowledge her sexuality, but also repeat that I would strongly advise her to wait until AT LEAST 16 before becoming sexually active in any way. (Explaining my reasons). I have also spoken to her openly about my strong objections to pornography, which she says she shares. (Of course we have all the blocks on her phone/the WiFi that you would expect, but we all know that a determined, intelligent, tech-literate teen can find a way around those at some point and view porn if she is utterly determined to, so a better bet I think is to help her understand why the porn industry is terrible and degrading, so she won't WANT to experiment with it).
I think "normal" covers quite a wide range - some people seem to develop strong sexual feelings/interest from around age 11, while for some this is only starting at around15/16 (or later/never in some cases).
OP, I don't think that the fact that your son and his friends are interested in sex is a problem in and of itself. But if I were you I would try to monitor the content of these discussions as much as you can, to ensure they aren't misogynistic; that no peer pressure is coming into play; etc.
If you appear judgemental, all you will achieve is encouraging him to conceal his views on sex from you.
Whereas what you want him to be is open and honest with you, I would think.
Also, it is developmentally appropriate for it to be just one of wide a range of interests. If he seems to be thinking/talking about sex to the exclusion of school work and other hobbies and interests, then I do think there is a problem which may require further exploration.
Good luck! Parenting is a bloody mine-field!.