should be OK. Even if part has been used. I've used West epoxy that was up to 5 years old.
I would suggest that, if you buy the kit, you do some test work with the epoxy and some scrap FG and ply.
And try to do the work in temperature above 70 degrees F. The epoxy will wet out the cloth more easily.
Oh, and if the kit is still in a box, does it appear to have been stored flat and kept away from moisture? You'll need to give it some time in a dry environment to give up moisture.
Any more details about the state of the kit?