As has been mentioned above, there are far more more important things to consider. I've bought a couple of semi-lemons and a couple of minters. Lots of lessons learnt and I'm fairly confident in how I'd choose a vehicle now. Main points I can think of ..
- Vet the seller. If he's an enthusiast, you meet him at his house and he describes the bike warts and all, you can be more confident
- Minimum number of owners (if there are problems it'll keep changing hands)
- Thorough service history, dealer or private (receipts, log etc). Only way apart from the test ride/listening to it to have an idea if the engine has had regular oil changes to keep it in top condition
- Not crashed! There could be hidden issues like alignment problems which have never been fixed.
If its a low revving bike like an SV, than a 60k miles bike like Jobs will be ok if it's been well looked after. If it's high revving than it'll probably have less life in the engine, but if it's been rigorously looked after by an enthusiast then it could still be in cracking condition.
It's still a punt no matter what.
My Gixxer has been crashed, has terrible service history and the owner wasn't exactly a passionate biker, although he was at least mechanically minded. As such, I got a bit of a lemon, but I knew that when I bought it. It was just a bargain and I wanted one so bad!
Even with all it's problems it's still been a cracking bike and hasn't cost me much to sort it. Engine is still good. Probably has 40k miles on it (can't be sure as the speedo doesn't work properly!). It's fine for my purposes because it's a weekend/hobby bike and not something I need to be ultra reliable.
Basically, mileage is 'meh!' if it's been well looked after.
The only other thing to consider imo is that 20-25k range where lots of consumables like chain/sprockets, bearings, valve clearances etc. might be due. If they've been done then that sort of bike is a better value purchase than a 15k bike of the same age which will be due all that stuff soon.