I have this one eyeliner, not sure how long I've had it. I'm thinking it might be time to throw it away, but I don't wear a lot of makeup and I finally found this one, but I can't remember where I bought it.
You should only keep products for 3-4 months. Although they have a longer shelf life, they are meant to be used before that. Generally someone who uses mascara (for example) every day will not have it for 2 years. It will be gone by then. you should be really careful with anything that is going near your eye and use only new products.
I keep mine for 1 year then I toss it after. There was a time that I continued using my eyeliner and mascara for more quite awhile since I don't really use it that often, I ended up having a sty on my lower eyelid. the doctor told me it can be caused by bacteria which can come from cosmetics.
It was awkward, going through my meetings wearing sun glasses in doors! lol....