The inexorable or the modifiable? Loss of our thymus by age 75, and loss of T-cell power.

It is our central immune hub beyond our spleen and lymph system, the thymus gland whose size vastly differs between age 20 and age 75.  Perhaps the shrinking is a sort of evolutionary enhancement, allowing for the new to replace the old, except for one problem.  If the only life span you can achieve is that of an insect, you cannot possibly achieve anything more than an insect.  So, our designed immune spans also align with what we are capable of (or allowed to do) by evolution.  Perhaps, if our efforts are not aligned with a universal design, our thymus will prevent us from building these warped designs, OR this is as good as it gets.  Probably, it is a match between finding what the universe wants from us, and knowing how to get around artificial limitations.  Potentially, thymic age is an artificial limitation imposed upon us.  Do we just sit there and accept such sadism?  Of course not.

Thymic involution

Apparently, thymic shrinkage is not a sealed fate.  Loss of thymus is very much why the older succumb to evil viruses more often than their younger peers.

As no surprise goes, our human botched gene for the very last step of vitamin C synthesis is behind thymic shrinkage too.  If whatever force that is alien to our advantage had not left us with a botched copy to remind us that we once had it, we may not have had to suffer the problem of thymic shrinkage with age and therefore shrugged off COVID-19 as just another cold.

High dietary intake of vitamin C suppresses age-related thymic atrophy and contributes to the maintenance of immune cells in vitamin C-deficient senescence marker protein-30 knockout mice.

Vitamin C is the gene rescue product you need to give humans, all of whom have a "nub," a reminder of what we all once had, a functional L-guluno-lactone-y-oxidase enzyme, which would have made us far more disease resistant, more resilient, and much higher functioning as the brain IS the greediest active sponge of vitamin C of all human organs.  It probably makes you taller too, if you are interested in that in your kids - really I never worry about that.