Yes, there's a certain shelf life for epoxy. Some of them are useless as little as 6 months after manufacture. The manufacture date and shelf life *should* be marked on the package if this is an issue.
Actually, I used to get a lot of great free CA glue and epoxy when the local shipyard restocked their shelves... Usually worked just fine for a good while after that. Thin CA turned into thick CA, and thick CA never cured was the only real difference.
