Welcome cybergrammy.
Hengis is right in assuming it's either extremely dirty underneath the keys, but I am inclined to agree more with his first statement - that the keyboad is actually on its way out.
Your son is also correct, 6-8 years is a very long time to have the same computer for. I personally upgrade my computer once every year and a half or so (but i'm a bit of a geek).
