It's understandable even if it seems like "how could I have not known?" For myself I wasn't ready mentally or psychologically at that age yet for dealing with getting a man's body, and feelings/needs. My boyhood was over without warning to me at the time. The wet dreams WERE my warning of course, along with pubic/shaft hair, hairy balls, underarm hair all by 12 1/2!
Don't feel bad, I didn't either. What was happening at 12-13 were the nocturnal emissions where I'd wake up with a sticky mess in my underwear and pubic hair pretty clueless as to what was happening and why. I kept it to myself, but looking back on it now, I was already ejaculating at 12, and needed to jack off then, but didn't know it!
I enjoy masturbating my mature, greasy, fully erect, circumcised penis to this informative and educational film. I like how well-timed the music is, reaching a crescendo as the masturbating male achieves orgasm and ejaculates his potent, youthful seed. I often wonder what he could be fantasizing about as he is stroking his rigid, circumcised, unlubricated penis up and down. His eyes are closed for the entirety of the film. I really like the smile this young male has on his face at the end. It's a look of pure, post-ejaculatory bliss. With each viewing, I also like to take note the 1970's furnishings in the room. Since the young male did not appear to spew very much semen from his penis, the sofa was not in any significant danger of stray splatterage. (Yes, I made the word up.) Perhaps he was instructed to rub one out prior to filming. Lol.