So, what do you look for if you find a fife that you suspect may be of early vintage? The first thing to look at would be the "tone holes", or "finger holes". The earliest tone holes seem to be fairly small, shaped about the same size and spaced rather equally apart. The edges are "sharp" and not "softened" by gentle rounding, as a general rule.
At some time, around the 1840s and into the 60s-70s, there appeared a space on some instruments between the third and fourth hole, so it looks like two groups of three. Also, at this time the holes become a bit larger and some makers started to bevel or "grade" the tone holes a bit.
So if the tone holes seem to be grouped in two sets of three, this would indicate a manufacture date in the 1840s or later. Spreading of the space between the 1st and 2nd holes (1st hole is closest to the "blow hole" or "embouchure") indicates a date even later.
If you find that the tone holes are of unequal size, research indicates a much more modern instrument.