Of course you can breed for resistance to gunshots. Size, hardened skin, extreme speed of ducking reflex, regenerative capacity, spiderlike weaving ability etc. etc.

Long term project, but in principle.

It works on fruit flies, see Rose, M. Laboratory Evolution of Postponed Senescence in Drosophila melanogaster. Evolution (1984), where the lifespan was doubled.

So this certainly works in principle. For longer lived species I expect it will still work, but it would take hundreds to thousands of years to breed for even a few dozen generations.

I would be concerned with secondary effects of aging on viability of gametes and chances of exotic conditions - doing this over any large span of generations would probably (temporarily?) yield a much higher mortality rate until we figured out the best ratio of increased parent lifespan to increased child mortality.

With humans you probably wouldn't want to wait with the breeding until the parents are old, but select breeding pairs based on the longevity of their (great-)grandparents. At least until you figure out useful biomarkers that reliably predict longevity already at the age of twenty or so.

> I wonder if it would be possible to breed for lifespan by breeding only the 'elders' among them

You wouldn't want to breed the 'elders' but the offspring of 'elderly' naked mole rats.