Old flame to get to 50 and celebrate (5)
I believe the answer is:
extol
'celebrate' is the definition.
(I've seen this in another clue)
'old flame to get to 50' is the wordplay.
'old flame' becomes 'ex' (an ex-partner).
'get' is a charade indicator (letters next to each other).
'to 50' becomes 'l' (Roman numeral).
'ex'+'to'+'l'='EXTOL'
'and' is the link.
(Other definitions for extol that I've seen before include "'Praise, glorify (5)'" , "Exalt" , "Praise enthusiastically" , "Highly rate" , "Praise greatly" .)