I shoot in our local IDPA matches so just for that I am going through 2500 rounds a year broke up into the several guns I use for that. Then I shoot weekly (when I can) and will shoot 50 rounds or so. My main IDPA Glock is a Gen 4 and probably has 200 rounds through it.
I have always laughed at guys worried about round count. The first time I ever thought of recording it was when we were issued a book with our Beretta's to log each round, each malfunction etc. That gun broke the frame at 3000 rounds. The H&K P2000 that replaced it went 15,000 ronds before I turned it in. Some guns will wear out quicker than others, some may just need a tune up, and some like AR's may just need an extractor and spring at 5000 rounds. I wore our a Remington 742 I shot it so much, wore the locking lugs off.
Buying a used gun is always a little gamble. Most people do not shoot as much as most on this board. Most guns will last a lifetime of casual shooting, a gun is no different from any other machine, if you use it, arts will wear and need to be replaced eventually.
My rifle and pistol are tools, I am the weapon.