I don't think ammo expires. so unless its in a moist enviroment I wouldn't think there is a limit.
as my CCW ammo is winchester white box, I rotate it out every time I go and shoot it. However often that is.(I use win white box 9mm because it's the only thing I've found to feed reliably, I need the gun to go bang when I pull the trigger. One of the reasons I carry a glock or an HK now instead of a 1911)
Hk usp, glock 19, browning high power, S&W something or other, beretta 92, never had a 9mm that would eat anything other than ball very well. Of course, my 1911 wont even eat that very well.
If your glock 19 won't feed JHP ammo reliably, you should give it to me for safekeeping.
It's a glock. It'll probably feed rusty corkscrews reliably.