I am now 40 so this took place 17 years ago.
I was 23 and was aked to help My Grandfather move into a retirement home. Grandmother had passed 6 months earlier but Grandpa atill wanted the big oak bed instead of the one that came with the condo. My Grandfather was 63 then and a big burly man, just like my Dad and just like me.
After everyone left I decided to stay overnight and drive back to Orlando the next morning. About 2am I get up for some water and hear the bed squeaking on the other side of the hall, not wanting to be noticed I entered his bedroom off of the master bath. There he was in all his glory jacking off...his barrel chest and silver fur along with his very large balls and good sized dick was too much for me. I dropped my shorts and started stroking right there. All of a sudden he yells 'GARY' what are you doing son? I said sorry and that I heard something and saw him masturbating. He said All guys do it and that it was allright if I wanted to join him on the bed. I came first and he laughed and said I would have to wait a little longer if I wanted to see him cum. I waited 10 minutes but it was worth it. I left the next morning and we have not mentioned it again in all these years but our relationship is as good as its always been and I still have good jackoff sessions thinking about Grandpa's cock and watching him cum.