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 - American Cream Ale, Darker Graf
Fermenting - Wee Heavy, Mead (split batch), ESB
Bottled - Purple Haze Clone, 7C's IPA, Cherry Cyser, Oktoberfest Ale, Lincoln Park Spruce Ale, Cherry Cider, Belgian Strong Ale, Pumpkin Stout, American Cream Ale, Wheat Graf