When genomic damage gets too significant, and damage occurs to critical genes, individuals do not survive to reproductive age, fetuses are miscarried and aren't born, or embryonic development breaks and it might not even be known that fertilization occurred.

Aren't there also mechanisms that reduce accumulation of genetic damage in gametes compared to the rest of the body? That helps too.

Evolutionary pressure can result in traits being selected over others because the individuals with the un-selected traits frequently fail to pass them on. But the cause and effect isn't so much "we need to survive this, let's devise an adaptation," it's "a certain trait happened to end up providing an advantage." There isn't an intentional aspect to the randomness of genetics.

Why and how would evolution - random mutation and selection pressures - penalize the long-lived? Many past cultures actually did the opposite, and elevated and respected elders, for their roles as knowledge holders and such. So how would being longer lived cause your progeny - who at that point would already be born - to be less prolific?

The human genome is clearly extremely well preserved and is has not changed all that much in hundreds of thousands of years.

However for an individual human, damage to tissues occurs.

For example, if you lose a tooth, it is not going to grow back even though you still have "tooth genes". And this damage is happening to every system of the body e.g. pretty much everybody has atherosclerosis and eventually all humans will die from it if they live long enough.

To increase human lifespan we have to fix all of this entropic damage, which is not impossible but requires advances in medical technology, such as growing new tissue to replace damaged tissue.