Grown-up holding a service, finally — worship (7)
I believe the answer is:
adulate
'worship' is the definition.
(I've seen this before)
'grown-up holding a service finally' is the wordplay.
'grown-up' becomes 'adult' (informal term for an adult).
'holding' is an insertion indicator.
'finally' suggests the final letters.
The final letter of 'service' is 'e'.
'adult' placed around 'a' is 'adulat'.
'adulat'+'e'='ADULATE'
(Other definitions for adulate that I've seen before include "Worship" , "Praise obsequiously" , "Excessively admire" , "Flatter obsequiously" , "Praise excessively" .)