The very first time I was ever truly by myself, alone, absent parental supervision, was my 18th when I flew from my parents house in Washington to my uncles house in Texas.
My birthday gift was getting to go to a proper beach, being able to drive a sports car (rented) by myself and other various activities my mom's brother decided I was entitled to do.
But my first jerking in public experience? I wanked on the plane ride. Right in the isle seat. I was so happy that my life was changing I couldn't help myself. It was a nighttime flight, and there were maybe 15 other people on the plane total, but I jerked it none the less. I wasn't shy about it either- my boxers (I wore them at the time) were around my knees and I let the cum fly all over. It was so liberating to feel myself cum, in public, at 36 thousand feet (or wherever.)