I'm still working on wearing out my first bike frame.
I've been working on it for the last 34 years, and I think it was over a dozen years old when I bought it, and it still hasn't worn out yet
I've seen a few broken and repaired frames, but not enough that I could state any statistics.
There seem to be reports of some riders that will tear bottom brackets out of steel and aluminum frames. Since these riders seem to be able to regularly destroy "modern" frames, and my older frame just keeps going... I do worry about all alloys including super-light steel tubing. And, there is a lot of discussion about aluminum fatigue... usually not talking about heavy MTBs.
Everything seems to indicate that CF is very resilient to fatigue, perhaps even better than steel and aluminum with the biggest wear type failure being Carbon Fiber -- Metal joints.
CF, however, is susceptible to impact damage (other metals may bend, but often remain ridable), as well as over-tightening (less so with other metals).
PLASTIC? I've seen a lot of ordinary plastic become brittle after a decade or so. I think the jury is still out on 10-20 yr old (or older) CF, and we may not have hit the maximum lifespan of a lot of frames.... yet.