Length of old Henry’s skipping torment! (3)
I believe the answer is:
ell
'length of old' is the definition.
(historical unit of measurement)
'henry's skipping torment' is the wordplay.
'henry' becomes 'h' (symbol for the unit of electrical inductance).
'skipping' indicates named letters should be taken away (to skip a place is to leave it).
'torment' becomes 'hell'.
'hell' with 'h' taken out is 'ELL'.
(Other definitions for ell that I've seen before include "Old cloth measure" , "Old measurement" , "Former measure of length" , "Length of cloth" , "approximately 45 inches" .)