Form of discrimination (6)
I believe the answer is:
ageism
'form of discrimination' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ageism that I've seen before include "Discrimination against the elderly" , "Resentment of the more experienced" , "Bad attitude to the grey" , "discriminating against the elderly?" , "The practice of treating people differently on the basis of longevity" .)