Does anyone know how long magazines last before the "wear out"?
That will largely depend on the use of the magazine and its initial quality.
Quality magazines like Pmag's, Glock mags, or steel AK mags should have a good lifespan of many years, maybe decades if properly maintained. Other cheaper mags may not last as long.
The frequency and type of use will also matter i.e. occasionaly range use vs serious competition or duty use.