As many others have mentioned… if you maintain your firearm it will likely last for tens of thousands, if not hundreds of thousands, of rounds which for most people is decades of use.
If you are curious about how some firearms stand up to HARD ABUSE, here are a few links on another forum where the owner of Battlefield Vegas talks about what fails on his firearms. If you don’t know, they rent fully automatic firearms so their stuff gets used and abused on a level I dont think anyone else can match.
High round count AR/M4’s (over 100,000 rounds)