Spoil bouncer, one in his 70s? (4,6)
I believe the answer is:
baby boomer
'one in his 70s?' is the definition.
(member of the baby boomer generation)
'spoil bouncer' is the wordplay.
'spoil' becomes 'baby' (synonyms).
'bouncer' becomes 'boomer' (boomer can refer to a male kangaroo).
'baby'+'boomer'='BABY-BOOMER'
(Other definitions for baby boomer that I've seen before include "born just after the war?" , "one arriving in a crowd" , "Joey" , "One of many born after WW2" , "Person born shortly after WWII" .)