For instance, nowadays, this exclamation seems old-fashioned (4)
I believe the answer is:
egad
'this exclamation seems old-fashioned' is the definition.
'egad' can be an answer for 'exclamation' (I've seen this in another clue). I am unsure of the remainder of the definition.
'for instance nowadays' is the wordplay.
'for instance' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'eg'+'ad'='EGAD'
Can you help me to learn more?
(Other definitions for egad that I've seen before include "Archaic exclamation of surprise" , "My word once" , "Mild oath - aged (anag)" , "Mild oath (archaic)" , "Christ" .)