Over and done with computers etc — too old (4,2)
I believe the answer is:
past it
'too old' is the definition.
(I've seen this before)
'over and done with computers etc' is the wordplay.
'over and done with' becomes 'past' (in the past).
'computers etc' becomes 'IT' (short for Information Technology).
'past'+'it'='PAST IT'
(Other definitions for past it that I've seen before include "No longer able, too old or decrepit" , "Informally too old to function" , "Far from fresh" , "Too old for task - gone too far" , "No longer in one's prime" .)