Experimentally, when I was 13, 14, 15. I was lean and flexible
and able to get a good half of it in, especially at 15 when I
think my cock was fully grown (it's long) or close to it. Helluva
feeling, much, much better than wanking. I remember thinking
I might choke cumming in my mouth, I shot loads of the stuff
quite a distance then, and I've always been a very heavy
precummer, and to self-suck best (get more in) I put my legs
over my head which was bent forward quite a lot. But I relaxed
and it worked. I was surprised at how sweet cum tasted.
When I was 16 I had g/friends who did it instead
I haven't tried since.