Our "wetware"--our brain--is something like a computer but not exactly. We can increase our RAM and the size of our hard disk, not by installing a bigger one, but the same way we increase the size and power of our muscles, by exercising them a lot. But muscles can only be built up to a certain limit. The brain's limitations are different. Sometimes it's just a matter of time to pay attention. My field is languages. Before I spent most of my time with foreign languages, I was a nearly perfect speller, maybe one mistake a year. Now because I occupy myself with half a dozen foreign languages all the time, I sometimes forget whether there are two E's in "saleable". (But I'd never forget most of the words that most people misspell, like isosceles, supersede or aficionado). It's just that I used to give lots of attention to English spelling, and now have to give attention to the spelling of half a dozen other languages as well. Until you begin dying, you can continue accumulating knowledge faster than you forget the old stuff. One new fact or memory won't push out one old one, but four or five new ones will push out an old one. In these other languages I'm always learning new words and forgetting old ones, but as long as I keep learning the number keeps increasing. That's providing you keep your mind active and exercised instead of just being a slouch on the couch.