I don't even know when I began, all I know is that I was doing it at 3 years old and most likely before. Before I'd use to do it and it felt good but I had no idea something could come out. So I one day I was doing it at 11 and suddenly something came out and I was like WTF and I thought too much masturbation caused it because nothing came out the last day or two. So I didn't do it for a while but later I had the urge again. Then I found out later what that something was and realized it wasn't something bad so I was happy.
Actually, back in 7th grade I thought the growing/shrinking of your penis wasn't right and I thought something was wrong lol.