He might not think that it is a good idea now. It might seem too much like a girlie idea to him. I think that If you start it, and by saving memorabilia, asking his opinion, he will begin to join in the activity. You might want to use a roll of film with fewer exposures so that the developing and scrapping will be more immediate for him.
A 5X7 album would be the perfect size. He will be able to tuck it into his back pack to take to school to show others his summer of 2002.
Most of all have fun with it. If he doesn't join in, at least you will have a great momento of his 10th summer.
chessie