95 12 valve with 248,000. Is there a mileage limit when the KDP won't fall out. or is it possible at any age/mileage?

 

It's possible at any time. It's just a metal post shoved in a hole that might be a little too big, so engine vibrations wiggle it around and it may move forward and fall out, or it may not. If you're concerned at all, just take the time to fix it.