I have no idea on the PRR, but in the Northwest, wood-sheathed boxcars lasted into the 70s. These were basically AAR cars with wood instead of steel sheathing, what many modelers call the "War Emergency" cars, although the GN, at least, was building them before the war.
For older cars, such as the USRA-style, and even earlier all-wood bodies, they seem to have been mostly gone by the early 60s, except in company or captive service. The pre-USRA cars probably wore out during WW II, and weren't worth repairing once the war traffic subsided.