Biofuel is a bit more than old! (7)
I believe the answer is:
ethanol
'biofuel' is the definition.
I can't tell whether this defines the answer.
'a bit more than old' is the wordplay.
'a bit' indicates a hidden word (I've seen 'bit of' mean this).
'ETHANOL' can be found hidden inside 'more than old'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for ethanol that I've seen before include "volatile flammable substance" , "intoxicating stuff" , "Ethyl alcohol" , "Kind of alcohol - not hale (anag)" , "constituent for a dram?" .)