It depends on a lot of factors, but some wooden guitars hold up pretty well, and it's glorious when you find an old-timer that's still usable.
I first became actively interested in folk music in the very early Fifties when Claire, the young lady I was going with at the time, developed an interest herself. She mentioned to her grandmother that she was going to buy a guitar and learn to play it, and her grandmother said, "No need to buy a guitar. I haven't played my guitar in years, so you may as well have it." Claire didn't even know her grandmother had a guitar or played one. Her grandmother went into a back closet in her house and emerged with a beat up old leather guitar case. It contained a guitar that was a dead ringer for this one, except that it didn't have a pick-guard. A "New Model" parlor guitar made by George Washburn. The date stamped inside the sound hole was "1898." Claire's grandmother said, "I think it's a good guitar. Your grandfather bought it for me for $50.00." That was a heck of a lot of money back in 1900. Needless to say, Claire was ecstatic.
The little Washburn was in excellent condition, but it did need a little work. The bridge needed to be re-glued (a paper-thin gap had developed under the back edge, away from the fingerboard), but once that was taken care of by a local guitar repairman and it was strung with a new set of light-gauge strings (some modern strings can pull an older guitar apart), it sang out loudly and sweetly for the first time in several decades. Beautiful instrument!
A few weeks after getting the guitar, Claire taught me G, C, and D7. Shortly after that, I went to a music store and, just for fun, shucked out $15.00 plus tax for a little plywood guitar, complete with fiberboard case, free pick (which I never used, because Claire played with her fingers), and a "How to Play the Guitar" pamphlet. And that altered my life.
By the way, the George Washburn "New Model" guitar that Claire had was no relation to the Washburn guitars that are made now. Completely different outfit.
Plastic would undoubtedly hold up better over a long time in inclement conditions, but a find like Claire's grandmother's old parlor guitar is a real treasure.