I've had mixed experiences with yeast 3-4 months old. Sometimes it has worked, others it didn't. Definitely make a yeast starter to judge the viability, and then you will have your answer.
JRBrewer on Untappd
Planned - GP/Mosaic SMaSH
Fermenting - Ned's Red (Flanders Red Ale), Saison Graf, Tangerine Mead
Bottled - Belgian Tripel, Belgo Graf, Saison (split batch with brett), Black 13 (Graf Porter), Old Style Amer. Cream Ale, Amber Graf, Wheat Graf, Bannockburn Wee Heavy, Berry Mead