i didnt discover mutual masturbation until i was out of town from parents at college. One thing i liked was the feeling of another hand on my boner. Becuase of that, i started masturbating with my left hand (i am normally right handed) It kinda felt like someone else doing it. Dont get me wrong, I love to masturbate, but love the feeling of sharing.
Three times, twice with my brothers. Once when I was about 11 and my older brother (13 yo) just casually pulled his out & started playing with it, then invited me to join. I did come, but it felt really weird, so wasn't repeated. Many years later, my youngest brother & I took a long hitch-hike around the country. I was +/- 30 and he would have been +/-24. In one city we went to a sex shop and in the back they had booths where you could watch porn and jack off. Once again, it was more weird than enjoyable. I've been at a sex party where everything happened, including masturbating. The idea of masturbating then was to keep yourself ready to fuck a girl who was pulling a train. so when your turn came you were ready and raring. I chickened out (didn't feel like sloppy 30 somethings), jacked off to completion, and left. Never been to another one of those, just not my cup of tea.