Male about 101 -- young member of family! (5)
I believe the answer is:
scion
'young member of family' is the definition.
(scion refers to a descendant of a rich family)
'male about 101' is the wordplay.
'male' becomes 'son'.
'about' indicates putting letters inside.
'101' becomes 'ci' (roman numerals).
'son' placed around 'ci' is 'SCION'.
(Other definitions for scion that I've seen before include "Branch" , "Issue" , "Young twig; descendant" , "Offspring" , "Younger member of a family" .)