age doesn't really have a whole lot to do with it- i've used threads that were 20+ years old & they are fine- i've had others i bought last week- that are not usable...
it depends on how they are stored, and the thread itself much more than the age- & just because you bought one last week does not mean it didn't sit around in a warehouse or store room for 10 years before going out on the shelves.
do a strength test- if it's still strong enough to use it's fine to use- if it breaks easily it's time to replace it.