I have a somewhat old acoustic that has an issue with the 13th fret on the high e. Fretting the 13th fret results in the same sound as fretting the 14th unless I give it a slight bend. Aside from a few dings, it's seemingly in good condition. Any advice on a possible cause and fix would be helpful. Thanks.
Either the 13th is too low or (more likely) the 14th is too high. Any decent guitar tech should be able to quickly put a gauge on these and determine which is the culprit, and then "dress" (file down) the offending fret.
Sometimes, the frets actually start to work their way out of the wood; in which case they can usually be repaired by either forcing it back down along with some glue or replacing altogether with a slightly-larger piece of fret-wire stock.