Grandson of Methuselah (4)
I believe the answer is:
noah
'grandson of methuselah' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for noah that I've seen before include "Animal rescuer" , "Early boatman" , "Biblical skipper during the Flood" , "Biblical shipbuilder" , "Old ship builder" .)