Hi Dianne,
If the eyeliner is still unopened, it should be fine for many years. Once products are opened, they will degrade since they've been exposed to air.
I usually keep pencil eyeliner for 2-3 years. If it's been a while since I've used it, I'll resharpen to expose new product.
If it's liquid (and has not dried up), I'd say 2 years should be safe.
I would go longer on foundation or blush, but don't like to take chances on any products that I'll be using close to my eyes.
Hope that helps!