"Ages" being? Months? Years? Decades?
They can go bad, despite the preservatives.
Some products have a little symbol of an open jar with a number on it, which gives you the amount of months the product is safe since opening it. Most of mine say 12 months. So to be safe it is advised to stick to that, but it's your call. I've used old products before without problems, but I'd rather not do it with anything that touches my skin.