Even telomere bound is not enough.
It's likely a set of advanced repair and local homeostasis so that feels still execute the complex maturing program correctly.
Too many senescent or damaged cells might just break the conditions... And mitochondria and cells have excellent mechanisms of dealing with reactive species they make, but sometimes chemicals leak in.
I'd be more concerned with infections and resulting damage at this point, plus toxic damage. Including endogenous like glycation.
And would there be a way you think to test if that's really the case?
I have talked with some people who had like severe reactions to the drug who managed to get some kind of mitochondria testing and it would say stuff like "30% of the active sites are blocked on the mitochondria"