[lossolo]

I think OP is not entirely incorrect. Reproductive cells undergo processes like epigenetic reprogramming, which basically strips away many of the chemical marks (like DNA methylation patterns) that accumulate with age. That’s one of the reasons babies don’t start with the cellular age of their parents. Researchers can take adult cells, reprogram them back to an embryonic like state using Yamanaka factors (a set of four genes) effectively erasing their biological age.

I think scientists currently are testing ways to "partially" reprogram cells to make them younger while keeping their function. Early studies in mice have shown some reversal of aging signs.

Seems like an engineering problem more than an absolute limitation.

[kingstnap]

DNA damage inevitably accumulates. The big reason children are younger than their parents DNA wise is because the parents' DNA undergo random recombination to create something that is the mixture of the two.

This doesn't help overall. Mixing two roughly equally broken things just yields the mean of the two. But the trick is that roughly 60 to 70% of conceptions will not survive to birth. This rejection sampling is ultimately what makes children younger.

If you had a population of single cells that didn't undergo this rejection sampling at some point, entropy and Muller's ratchet would actually age the entire population and kill it.

[lossolo]

You are right that DNA damage inevitably accumulates and that selection (including miscarriages) weeds out embryos with severe defects but that doesn’t fully explain why a newborn’s biological age is near zero.

What scientists usually mean by "cellular age" isn’t mutation load, it’s the epigenetic and functional state of cells. During gametogenesis and early embryonic development DNA undergoes extensive repair, telomere maintenance and global epigenetic reprogramming that wipes and rewrites methylation patterns. This resets the cellular "clock" even though some mutations are passed on.

So while mutation load drifts slightly each generation, the reason babies start biologically young is this large scale reprogramming. That’s also why researchers are trying to mimic this process in adult cells (Yamanaka factors etc) to reverse aspects of aging.

[hallole]

Fully agree! I don't think life is much more than a sort of chemical engineering, "designed" with the "purpose" of self-replication. Our engineer, natural selection, didn't have "healthspan" in mind; insofar as we are human-making machines, we're pretty well built. I fail to see any reason that necessarily precludes a retooling of our internal machinery to accomplish our desires, not nature's.

[XorNot]

More over, babies can clearly grow from limited cells to "young" versions of fully differentiated human tissues. Which means from some initial stock, you can replace the vast majority of the bodies cells with younger versions - i.e. with plausible, attainable technology we would generally expect to be able to grow immunologically identical replacement organs and major tissues. That definitely is an engineering problem, more then anything else.

The only truly troubling one is the brain, and we're very much not sure if it actually is one or for example, suffers degradation from the degradation of the body its attached to - likely both - but we also know that the brain is not a static structure, and so replacement or rejuvenation of key systems would definitely be possible (certainly finding any way to protect the small blood vessels in the brain would greatly help with dementia).