I gave most of my old stuff to my mom and sister. It was still good, but I just wasn't using it, so I passed it along.
Now, my oldest MAC item is my Parrot eyeshadow.
But, previously, there was stuff I'd had since I was in high school (I'm 26 now) that was still good.
So, yeah. You don't have throw stuff away after a few years. If it still looks the same (or in the case of lippies, still smells the same), then it's fine.