But, unfortunately, all the ones we know of can be skewed by environmental factors. And it is likely that the exact same environmental factors which make someone live longer will also make them appear younger than they are. Which makes them particularly unreliable exactly for the oldest people on record.
Even cells that don’t multiply still accept nutrients. Pretty much no atoms in our bodies stick around for too long. It’s why carbon dating largely measures the time an organism died.
Mineral deposits in our bodies (teeth and bones) are pretty good.
In non-replicating cells DNA would be pretty good too. Some of it gets replaced as repairs occur, but most of it would not. I'm not sure that carbon dating would be very accurate over the lifetime of a person (though specific events could cause specific sorts of deposits in bones during the occurrence of those events). And even if it was, radioactive carbon, either because of damage, or because of electrochemical effects, would probably be replaced in DNA more frequently than non-radioactive carbon, as long as the organism was alive, even in non-replicating cells.
This doesn't hold true for all cell types. There's a group in Sweden that has C14 dated the replication rate of some cell types. IIRC some cell types - some neurons and adipocytes - only replicate every 10 years or less. Their method has something to do with C14 from nuclear weapons: people who lived before they went off wouldn't have as much. And a lot of C14 would be from the uptake of nuke C14 since. IIRC pre-nuke people have adipocytes with C14 amounts compared to post-nuke people because those cells barely divide. That's what I picked up from a talk way back. I believe this is the same group.
https://news.ki.se/new-neurons-generated-in-the-hippocampus-...
I agree we could find markers of age, but I think they'd be nothing like tree rings, which are created by the freeze-thaw cycles and the fact that they are fixed in one place and exposed to the elements in ways humans are not.
Although, that begs the question, if a potted tree were to be placed on a cruise ship, which always sails to warm weather, would it fail to develop rings?
Trees in tropical climates don't have rings because they grow year round. If you took a tree that normally has rings to a climate where it would not be exposed to hot and cold, the tree would either die or not have rings:
For example, there are certain cells that don't multiply after birth (eg. some nerve cells). One could presumably date carbon atoms in their DNA...
Or parts of the body that don't regenerate - like tooth enamel.
I suspect with the right type of imaging, you'd probably find 'tree rings' in things like fatty deposits in arteries too.