As a generalization, I would suggest "new bikes wear out faster than old ones." Once upon a time bikes were made to be repaired, rather than replaced. And it is still easier to repair old bikes than new ones. Aside from that, steel frames basically don't wear out. They can get damaged, of course, but they don't weaken over time. I have had aluminum frames fail after a few years of use; it appears the metal fatigued eventually. I don't know about carbon.