New to Glock magazines, but my colt 1911 mags stayed filled for over 5 years (I had three) and stood up to almost weekly trips to the range and through quite a few informal local range competitions. Never had a failure.
I've already bought 3 extra mags for my Glock and plan on getting a couple more. I keep two loaded with SD ammo and the rest loaded with range ammo because I often go at the drop of a hat and it's nice to be able to run off 50 rounds without having to reload anything.
They're cheap enough that I'd just grab a new one (or two) every year and rotate the older ones out if I were worried about it, but I'm not there yet.
Just keep them clean and I wouldn't worry about it.