100-112 yrs. old, according to some non-canon info I found.
64 years old.
look at her with the mask of truth to find out
Which Impa, theres like 3 Impas in the series
^ Actually, there are about four Impas in the series, unless you count Impaz on Twilight Princess as one, then there are five. Timelinesplitter 02:06, June 8, 2012 (UTC)
In the case of Old Impa, about 94.