Well, If you don't want to ski with your old man, just don't. But remember,
it's all time you'll be spending with him. When you'll get older you'll have fond memories of the time spent toghether. I think that it's called "quality time" for us parents. Why shouldn't it be the same for you "children" ?
I'm a better skier than my mom and uncles, always been, even now that I'm 43, but that did not stop me skiing with them, on the opposite, I was the "example" to follow for them, and for me it was a joy to spend time with them. It still would be, I miss skiing with them.
Beyond that, my mother did invest a lot of time and money, money she could have sepnd to improve herself, sending me to ski school. She deserved something back.
My son is a better inline skater than me (he's a racer) but this doesn't stop me from wanting to skate with him and his brother.
Same for the other son, we go to the swimming pool and swim toghether, he soon will be better and faster than me, but I hope he still will want to come with me.
As for skiing, I would love to see them both become better than me!