15 when I was physically immature for my age and had never heard of masturbation at school.
My best friends younger brother who I will call Ben and I were alone on the banks of a river. He was nearly 14 when he asked me if I 'did it'. I was embarrassed as I had no idea of what he was talking about. I remember he explained about masturbation and asked if I wanted to try. I said yes and next thing I know my shorts and jocks were down to my knees...he wrapped his hand around my small penis and started the up and down motion we all know. I got bigger and swear it took ages for me to feel anything at all of note. Eventually the most amazing feeling came over me, I tensed up in the throws of my very first ejaculation. I cannot remember how much was expelled or indeed where it landed because I was in heaven. I don't think I have ever cum close to that first time. It was amazing and something I will never forget.