Previous maintenance history means a lot more than mileage. My '76F has about 40k miles when I got it. I put another 10k (hard) miles on that bike and it was fine. 100,000 miles on sohc CB's is not unheard of. Later model CB's like you are looking at will go just as far if maintained well.
If the engine is quite,smooth and runs/revs well it's probably ok. Check for normal signs of wear: burning oil, oily tailpipe inside, puff of oil smoke on cold startup,etc. If you are really concerned ask if you can perform a compression test.
Rpms and miles don't hurt them. Neglect does. Just try to decide if the bike you are looking at has been owned by a responsible person before. Good luck!
edit-Tools snuck in on me