I remember my first orgasm well, I hit puberty early so I was looking at softcore porn aged 10/11 in 2002/03. I think my first orgasm was early 2004, I was humping my pillow and I felt this strange feeling, I ran to the toilet and my legs buckled, liquid came out of my penis and it was pleasurable. However I don't think I started masturbating to late 2004 aged 12 when my foreskin was able to pull back fully. Up until 2006 I used to masturbate and when I was about to cum I took my hand off my cock and came hands free, I then realised that if I kept jerking when ejaculating the cum would squirt out, before that the cum would seep down onto my pubes.
I have quite slow semen production, I can only ejaculate twice a day or 3 at an extreme. Maybe the semen is there but I can't get horny enough to ejaculate it.