The stability of the dyes may depend on the storage conditions, but I think fading would be most heavily influenced by the amount of use rather than just age.

Regardless, it might be a good idea to get a new set anyway, especially if you don't have the latest version. You can tell by looking at the 00 and 5 filters. In the more recent sets, the 00 is no longer yellow, but a more orange-ish colour, and the 5 doesn't look as "purple" anymore. And the newest Ilford papers are really optimized to work with the latest version of the filters.