A while back I fell down the anti-aging rabbit hole, and it was fascinating to realize that we have no good way to measure aging. We can measure different things that seem associated with it, but I guess since we don't know the root cause(s), we don't have any one thing we can all agree on. It seems like the only thing everyone can agree on is that if a person looks old, they (probably) are.

Which is a long way of saying, yes, I agree with you; the methylation metric may be total bunk. But there isn't anything else (IIRC) that we can all agree to measure instead. That's why the Harvard article emphasized that they were using a metric for aging they'd developed in-house. I just want to read the paper before passing judgement, and right now sci hub doesn't have it.