It all depends on how it is ridden and maintained. Someone once wrote that if a modern car was maintained like a jumbo jet, it would last 10,000 years. If your bike is ridden sensibly, maintained properly and never involved in an accident, I reckon a good 10 years at least. I have a 7 year old Yamaha YZF600R which still looks like new, 45,000 miles and sweet as a nut. I'm a marine engineer and a stickler for things being right, so she got a full chassis rebuild last year. My 1200GS has 18,000 miles on it but it is only a year old so I had better start taking things easy if I'm going to reach the ten year mark with her.