He was thirteen
My son and I live together by ourseves. We often walk around the house naked. One time when my son was getting out of the shower he asked me how do you masturbate? I said let me show you, go into your room and I will be right in there.
So I went to my room and took off all of my clothes and got some lotion and went into his room. I said just do what I am doing. I put some lotion on my hand and went at it. After a few minutes he did the same thing. In about two minutes he came all over himself. I did as well about two minutes after him. We did it a few more times after that. He is getting a lot better at it.