I dunno, in a way i would still say snooker is more of a game, but then i don't know, the line between games and sports are kind of fuzzy.
I would say that a sport needs to have some sort of physical exertion. In that respect then yes a proper game of golf is a sport as it requires said physical needs.
That is why in golf you find your handicap begins to rise again as you get older etc. As far as darts, it does not matter how fat or old you are, you will still be able to throw a dart.