I've used expired kits.
Reconstitute the concentrate , then taste the juice. If it tastes like fresh grape juice with no obvious off flavours, then your probably good to go.
If the juice tastes bad, then your not going to get a good result. (this is true of any wine kit regardless of age)
There may be a bit of crystalized sugar in the concentrate, just use a bit of hot water to dissolve.
You probably want to get a fresh packet of yeast as cheap insurance
I dont normally use the finings in the kit, but i believe the keisol and chitosan could go bad in time. I'd leave those out, just to be safe.
The other usual components of a kit are sorbate and metabisulphite, both preservatives, so they shouldnt go bad.