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.
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.
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.
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?
https://scied.ucar.edu/learning-zone/how-climate-works/tree-...