That's what happened.
When I was a young teen I asked my step-dad about cock sizes and all. He was real tired sitting in his big chair but he took out his cock and got a hardon and let me fondle his cock and balls.
I guess I was too vigorous 'cause I accidently masturbated him, with his cum shooting on his work shirt. I was scared but he said that was OK and I really should ask his son, my 17-year-old step-bro, about what I wanted to know.
I rarely saw him because he was always busy with school and sports, but one day we got together and masturbated each other. We did more but this is all I will say. We were jack off buds until he turned 18 and joined the Navy.
My step-dad and me were the only guys at home except for mom. He was real cool, he was only 39, and he would let me jack off to his pic mags in the garage. Sometimes he would join me and we would spurt cum like no body's business.