Groups age on dope (6)
I believe the answer is:
genera
'groups' is the definition.
(more than one biological genus)
'age on dope' is the wordplay.
'age' becomes 'era' (both can mean a long time).
'on' says to put letters next to each other.
'dope' becomes 'gen' (both can mean information).
'era' put after 'gen' is 'GENERA'.
(Other definitions for genera that I've seen before include "Groups between family and species (biology)" , "Types" , "classes" , "Biological groupings" , "Categories making up a family" .)