It really depends more on previous ownership. These bikes are often owned by a younger demographic that doesn’t know how to take care of it or by folks who consider it a cheap bike not worth their attention. My first 300 had 17k miles on it when I bought it and the list of things I didn’t fix would be shorter to write than the other way around. But with proper care you can expect to exceed 60k miles or more. I have seen posts from people showing in excess of 100k km, mostly from Europe or Asia, as I recall. I’d say take a close look at the bike. Does everything work and is in good condition? On the other hand, rusty chain? Walk away. There are 300s in good condition out there, and unless you want a project I’d wait for the right one.

 

Hogges is spot on. When I bought my little Ninja 9 years ago with 2700 miles I thought you had to get a low mileage bike. Now I realize that with proper maintenance a bike with 20, 30, even 40K miles can be a great buy. 2 years ago I bought a 39 year old Honda Nighthawk 650 with 21K miles...refreshed everything on it and it is a reliable daily ride, if needed.

Lots of good youtube channels out there showing picking up old, rusty, crusty bikes and getting them back in good running order. Long story but bikes are good for many more miles than most people think.

 

As noted - it will vary a lot.

Look at the chain. If it has a sloppy rusted chain, it shows that they were not serious about maintenance. Also look at the color of the oil. If it looks like crude, again, not proper maintenance. Brake fluid should be clear or just slightly yellow.

Tires should have been replaced by now. Look at the date code (4 numbers in an oval like "2615" - the 26th week of 2015). Be prepared financially to replace tires that are over about 5 years old.