I first learned about jacking off at 13. I watched my dad, who was 34 and naked, stand in front of the bathroom wash basin and ejaculate into it. He had an athletic body and, I learned later, an eight inch by six inch uncut cock. I could see him clearly through a small hole in the bathroom door. It was a beautiful sight and erotic.
I watched him masturbate like that until I turned 18 and moved to my own place. I would jack off watching him masturbate. Many times we would ejaculate at the same time. I think he knew I was watching him.