As my friend Bob puts it, now that I've reached "advanced middle age," i.e., that would be pressing almost 7 decades on this planet, I can't remember shit. There's a wide, real wide, variety of health issues that people have at this stage of life, but there's one complaint that's universal. The older you get, the less you can remember. What's clear is stuff that happened years and years ago. What happened yesterday . . . well, not so much. This piece I ran across offers an explanation.
According to Michael Yassa, a neuroscientist at Johns Hopkins University, the reason things get tougher to remember as we get older is because the pathways leading to the hippocampus degrade over the years. Since the hippocampus is where memories are stored, it makes sense that with age our brains just find it more and more difficult to process information we receive into things we remember.
In essence, it's not that our brains are "filling up" with information; it's just that our brains get less effective at writing and storing that information as we get older. It's the reason, according to Yassa, why we're so nostalgic as we get older: it's just easier to look back on memories our brains have already stored than to create new ones that are just as vivid. At the same time, Yassa's research doesn't suggest how we can fix the process; only that the research could be useful in treating Alzheimer's in the future.