Fellow of 50, nowadays (3)
I believe the answer is:
lad
'fellow' is the definition.
(I know that fellow can be written as lad)
'50 nowadays' is the wordplay.
'50' becomes 'l' (Roman numeral).
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'l'+'ad'='LAD'
'of' is the link.
(Other definitions for lad that I've seen before include "Boy or youth" , "Stable employee" , "Chap, fellow" , "A young chap into ballads" , "Young fellow" .)