One of an older generation having son react badly (8)
I believe the answer is:
ancestor
'one of an older generation' is the definition.
'son react badly' is the wordplay.
'badly' indicates anagramming the letters.
'son'+'react'='sonreact'
'sonreact' anagrammed gives 'ANCESTOR'.
'having' acts as a link.
(Other definitions for ancestor that I've seen before include "Old member of the family -no traces (anag)" , "Predecessor" , "Person from whom one is descended" , "descent comes from one" , "not being of the modern generation" .)