Type of discrimination (6)
I believe the answer is:
ageism
'type of discrimination' is the definition.
(I know that ageism is a type of discrimination)
This is all the clue.
(Other definitions for ageism that I've seen before include "Non-PC attitude to senior citizens" , "Prejudice against senior citizens" , "Discrimination e.g. against old people" , "Images (anag)" , "Form of discrimination" .)