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....
Not a Fleshlight, but I have a comparable masturbation toy called Tenga 3D. Smaller and less expensive than Fleshlight and comes in five varieties of texture for different degrees of stimulation. I have three of them and love edging for hours with them.
I did it occasionally, when I was still doing M/M hook-ups. Lots of guys who are into gay-sex think it looks sexier. I think it shows off my smallish cock better. And then there's the fact that many male porn stars shave (along with ALL of the female porn stars).