A strict diet won't be too much for him.  It just might make him into a brand new dog!  It's just that he's probably like the rest of us, and as he has gotten older and wiser, he has learned which buttons to push to mooch a snack.  )

I don't think ten years old is too old either.  I realize big dogs don't usually live as long as small ones, but there's no reason not to expect him be healthy into the early teens, even with a few aches and pains.  8)