If you're only a couple decades old, you probably haven't experienced too many problems with your memory. But if you're more than a few decades old, you might have started to get "senior moments" as some call them -- where you forget why you went upstairs to your bedroom as soon as you get there, or you can't remember your ATM PIN, or the name of that guy is just on the tip of your tongue but you can't seem to recall it. These could be early signs of more serious memory loss, but the medical science is only just about to start really understanding how memory and aging works. Here are some links you might want to check out (and bookmark so you don't forget them).
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post