We don’t know why older adults perform poorly when their neural activity suggests their memory capacity is intact, but we have two leads," Ko said. "First, further analysis of this current dataset and other studies from our laboratory suggest that older adults retrieve memories differently than younger adults. Second, there is emerging evidence from other labs suggesting that the quality of older adults’ memories is poorer than younger adults. In other words, while older adults might store the same number of items, their memory of each item is ‘fuzzier’ than that of younger adults." ~ Younger People Have “High Definition” Memories : News : Parent Herald.
I’ve always had a simple theory for why older adults have poorer memories.
First, I agree that it likely has something to do with the brain simply deteriorating in some way. I think that’s pretty safe to assume.
But I doubt that’s the main issue.
I think the main issue is that young people throw everything into memory creation, storage, and retrieval. I think they do this because, like a young rattlesnake, they don’t know how to prioritize and control their poison.
Basically, I think young people treat all memories the same, i.e. as high priority, because they don’t know any better.
I think older adults know very little is important and start subconsciously ignoring most things while trying to maintain a set of important things at all times. Mortgages, bills, kids’ whereabouts, etc.
I think this pull on their faculties causes many memories that kids would excel at recording and recalling to simply be missed by older adults.
TL;DR: Kids store everything because they don’t have much to store and haven’t started ignoring things yet due to the responsibility of adulthood. Adults are burdened by responsibility which force them to store memories in low definition or not at all.