Ship's grand age with everybody on board (7)
I believe the answer is:
galleon
'ship's' is the definition.
(I've seen this before)
'grand age with everybody on board' is the wordplay.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'age' becomes 'eon' (I've seen this before).
'with' means one lot of letters go next to another.
'everybody' becomes 'all' (I've seen this before).
'on board' means one lot of letters goes inside another.
'g'+'eon'='geon'
'geon' going around 'all' is 'GALLEON'.
(Other definitions for galleon that I've seen before include "Historical warship with three or more masts" , "Trader" , "Ship of the line" , "Large old sailing vessel" , "One might sink" .)