Could it be grandfather, white-headed — I'm blown away! (5)
I believe the answer is:
clock
I believe this clue is a double definition.
'could it be grandfather' is the first definition.
(as in a grandfather clock)
'white-headed i'm blown away' is the second definition.
(clock can mean the head of a dandelion)
(Other definitions for clock that I've seen before include "Time-teller" , "Watch" , "Hit" , "Timepiece" , "Notice" .)