Close to four, old boy elected to prepare vestry (6,4)

'vestry' is the definition.
(a vestry is a church robing room)

'close to four old boy elected to prepare' is the wordplay.
'close to' says to take the final letters (the close of something is the end).
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'elected' becomes 'in' (in government).
'to prepare' becomes 'groom' (eg grooming someone for a job).
The last letter of 'four' is 'r'.
'r'+'ob'+'in'+'groom'='ROBING ROOM'