The scholar takes ages to sum up (7)
I believe the answer is:
erasmus
'the scholar' is the definition.
(Erasmus is an example)
'ages to sum up' is the wordplay.
'ages' becomes 'eras' (I've seen this before).
'up' is a reversal indicator (in down clue: letters go upwards).
'sum' in reverse letter order is 'mus'.
'eras'+'mus'='ERASMUS'
'takes' is the link.
(Other definitions for erasmus that I've seen before include "Desiderius -, Dutch scholar, humanist" , "Dutch mediaeval humanist" , "Learned person" , "He praised folly" , "Old theologian" .)