Caught 13 year old son naked with his 13 year old cousin (boy)

I was about this age in the late 60s. Back then, anal sex wasn't completely unknown, but it was thought of strictly a gay (and that wasn't the term they used back then) thing. But this is today, and today, if a boy goes on-line to look up fun things a couple of naked guys can do with each other's bodies, anal sex is probably just portrayed as one of the options, so I wouldn't worry about the son being gay, but I would worry about where he is getting his sex info. I would like to direct 13 year-olds to sites that limit it to shaft pumping, head rubbing and lubrication. Unfortunately I can't tell you how to find sites with these limitations. If you want realistic naked people, look under "Vintage nudist".
If I caught my puberlesent son looking like he was about to engage in anal sex, I would warn him about this; That hole back there is called your rectum. Your rectum has microorganisms in it. They're just fine where they are, BUT if they get into your reproductive system, they can raise hell. So don't go sticking your penis into anybody's rectum, because if you do, those microorganisms will be crawling up the tube you pee through and into your bladder and testicles (and a few other things with names that I don't know), and screw them up. And IF they can be fixed, it will take a doctor and medicine. Trust me, It's more trouble than the fun is worth.

Yes it's still normal. I used to have mutual anal we with my younger cousin and we both turned out fine

Its normal a lot of us al did the same thing . Its hard for a female to finger out how our minds work as it is for us to finger out hoe a female mind works . And I say again its normal for us to be curios about sex . Some as young as 11. tel the you forgive them and you will forget about it .

It is just the natural thing to do: explore and investigate and to have fun learning! "Learning by doing and not by reading" is the best way

yes yes yes

when i was young,boys behind the school bike shed shed would
compare penis sizes ,masturbate each other. to me it seemed
natural and very exciting

my first sexual experience .when my male cousin stroked my very erect penis .my first sexual venture at 13 years old very enjoyable

no big deal .young boys to make genitalia contact. its part of their
development

when young people reach puberty,the will coerced by their peers to get involved some form sexual activity

This is one which leaves me saying. "I wish he read his submission and did a re-write before hitting Reply."
Here's what I think the story was; He and his 13 year old friend spent the night together nude after sex-play but without ejaculating. He must have been a very sound sleeper and his friend must have reawaken first and went for another round of sex-play with his very erect penis. (Having your best erections while asleep is very common, as any guy who has awaken suddenly can tell you.) With that head-start, this round of sex-play did produce one or more ejaculations. When he did wake-up, he found the area around his penis covered in seamen.