18.
I wanted to try it out for fun.
No one taught me, it was an adventure lol.
I used a disposable razor.
This was 1991, guys shaving was, as far as I could tell, just not done. I was in university then and I actually stopped going to the school gym until it grew out some because I always showered there and didn't want to show my clean shaven crotch. I did however started keeping the sides and shaft shaven. On occasion I would remove everything. When I graduated in 1996, I kept it very, very trimmed - everything but above the penis itself, and I kept those hairs very short. I went to a gym where nudity in the locker room was very common and the showers were open. There was one guy that was always bare, so I thought that if he was okay showing everybody his shaved crotch I would be too. So I started taking everything off. I was still very self conscious doing this however so it was only once in a while - other times it was heavily trimmed. Still seeing other trimmed men was very rare. I started going to the YMCA in 2000 and that's where I saw a lot more trimmed guys and even some shaved ones, and that's when I decided to be bare all the time.
I started laser hair removal last year, it's basically all removed now - shaft, front, scrotum, anus. Being bare/heavily trimmed is definitely much more popular now.