A weekly gay orgy in the basement of a middle-class house in my city. Advertised in CraigsList and screened who they gave the address to. Mandatory nudity, except shoes optional. $10 admission at the door. Usually about 20 guys of diverse ages and races. Sucking, jacking, fucking pretty much constantly. Lasted 90 minutes and was at lunch hour, so I could be cool with getting back to the job.
I almost did it as a teen, when I was playing around sexually with boys. Had a long stretch of being married/monogamous. Finally did anal, topping and bottoming, when I was in my late 40s and exploring my bi-side.
Some no-reciprocation cocksuckers can't get erect themselves and figure (probably correctly) that their partner wouldn't be satisfied sucking a soft dick. But they get off on doing the sucking, and they make the recipients happy.
I was 13. Naive about orgasms, but I knew it was fun to play with my boner. Three similar-age boys in the neighborhood asked me to join their 'Sex Club'. I was a shy kid, but I immediately said yes. Since I was the newest member, they said I had to do 'the initiation'. It consisted of stripping naked and letting the other guys feel up my boner and balls and ass, and then sucking each of the guys for 30 seconds each. I liked it immediately, having a hard cock in my mouth. Had my first masturbation that day too. It didn't take long before I was sucking one of the guys to a spurting completion, and him sucking me likewise. (The other two hadn't hit puberty yet; not as fun to suck.)
"Pure sex" indeed. Nothing quite like it.
Note, however, that glory holes play especially well to the desires of closeted bisexuals (like me). Totally anonymous but affording a unique sexual experience.
When I was young, I never used lube... just a light touch in stroking. But I never lasted very long. Now that I'm edging for at least an hour when I masturbate, I always use lube. My favorite is Astro Glide.
If there was a group-shower room for school athletics, like back in my day, boys would get over their shyness in an instant (unless their penis was unusually small or large, or they always popped an erection in the showers).
When I was 19, I was visiting a friend and sleeping on the living-room sofa. I woke as one of his house-mates was pulling off my underwear. I pretended to be asleep as he played with my cock and then sucked me off. I wish I hadn't been so closeted back then, or I would have "woken up". (I was very conflicted and shy about my fascination with gay sex.)
What's too young? Whatever the law says. I was having sex at 13, though not with adults. And I am still attracted to young teens, but I would never violate the law or coerce a hesitant partner. But if I were in Japan, and a precocious 13-year-old boy or girl was trying to seduce me... well, uh....