Experienced apostle's heading off in front (7)
I believe the answer is:
veteran
'experienced' is the definition.
(I've seen this before)
'apostle's heading off in front' is the wordplay.
'apostle' becomes 'peter' (Peter is an example).
'heading off' means to remove the first letter.
'in' is an insertion indicator.
'front' becomes 'van' (I've seen this before).
'peter' with its initial letter removed is 'eter'.
'eter' going inside 'van' is 'VETERAN'.
(Other definitions for veteran that I've seen before include "An old hand or ex-soldier in USA" , "Experienced ex-serviceman" , "Old hand, ex-service person" , "One with lengthy experience in service" , "Old; experienced" .)