You're not wrong, but your models of aging events seem to be too simplistic. Aging is not one process but a complex of interacting processes. There are definit

You're not wrong, but your models of aging events seem to be too simplistic. Aging is not one process but a complex of interacting processes. There are definitely a number of processes involved in aging that are pre-programmed as you suggest, namely the hormonal clocks involved in puberty and maturation, and then later senescence. It's not particularly useful to compare humans/mammals to single-celled organisms, which operate under way fewer constraints. They don't have to deal with cancer, as just one very basic example. They also don't have to figure out how to clear old junk from their tissues and individual cells. They just start over with a clean slate every time. Signals in the bloodstream - various hormones and immune cells - are obviously involved in aging. But there are many of them, and we are just starting to understand their different interactions. There is no doubt that aging research is going to yield ways to suppress or promote the action of certain hormones, replenish/reactivate certain stem cell populations, etc. but better understanding of intercellular regulatory networks is needed for that. To call DNA methylation the determinant of an "aging clock" is also too narrow or simplistic. DNA methylation is the mechanism of cell differentiation, but it's "metadata" that has to be copied over between cells when they divide, just like the DNA itself. Early in embryogenesis, the DNA methylation pattern is reset and overwritten using the regulatory cascade of master control genes (homeobox, etc.) - so it is expected that the methylation pattern will have lower fidelity with each division cycle before or after that point. This is the golden age of biology - we have just gotten a hold of the tools that will let us solve these problems - but it's messy and complicated. Investing in your understanding of these processes can have a huge payoff - I recommend reading some of the Nature Reviews articles like https://www.nature.com/nrg/ https://www.nature.com/nrg/ - I've always found them to be incredibly helpful in summarizing the state of the art.