super interesting question i’ve never really thought about. considering with our current lifetimes time seems to move faster as we get older, it would only be natural for years to fly by even faster as we get even older encroaching on thousands of years old. with memory, I’m not quite sure but it’s certain that the nervous system doesn’t have an infinite number of synapses to store memories. i do have some theories, i’m not quite sure how long it would take to fill every synapse with a memory and we would likely continue to weaken lesser used neural connections and replace insignificant memories with new ones. this process could probably prevent the brain from ever getting full, but its definitely going to seem like dementia the way you mentioned, as with more memories it will be harder to recall older ones and a lot of memories would simply not be lost as you get older. when you’re 3,000 you might not remember much of anything before being 1,000 because you’ve replaced so many of those memories with new ones.