a bike can last a long time as long as you do these things on top of not abusing the living shit out of the bike:
-oil changes every 2-3,000 miles
-scheduled tune-ups (plugs and power packs and VALVE ADJUSTMENTS) whenever the factory recommends
-change your sprockets and chains when they start to wear out (hint:if your chain is so stretched u need to take links out, its time for a new one)
-keep your brakes good
-get your carbs cleaned (for those who apply)