The mixture may separate, but simple agitation will fix that. However, over a number or years, the linseed oil may polymerize and become a sort of insoluble gum. If you paint with any frequency, you'll use all the product long before it goes bad.
That said, I have a couple tubes of Liquitex-brand oils left over from the '80s and they're fine, while I've had paints within the last decade that have polymerized. So your mileage (kilometrage) may vary.