Character billed as old and decrepit — nothing to it (6,4)
I believe the answer is:
donald duck
'character billed' is the definition.
I can't tell whether this definition defines the answer.
'old and decrepit nothing to it' is the wordplay.
'decrepit' is an anagram indicator.
'nothing' becomes 'duck' (duck means zero in cricket).
'to it' says to put letters next to each other.
'old'+'and'='oldand'
'oldand' with letters rearranged gives 'donald'.
'donald'+'duck'='DONALD DUCK'
'as' is the link.
Can you help me to learn more?
(Other definitions for donald duck that I've seen before include "Bradman getting no runs" , "bird apparently brought to life" , "Disney cartoon character" , "Walt Disney character" , "would be a figure of fun" .)