Young people who never say no to food? (7)
I believe the answer is:
yuppies
'young people who never' is the definition.
Although both the answer and 'young' are nouns, they are not in the same form of the noun.
'no to food?' is the wordplay.
'no' becomes 'yup' (I can't justify this - if you can you should give a lot more credence to this answer).
'to food?' becomes 'pies' (I've seen this before).
'yup'+'pies'='YUPPIES'
'say' acts as a link.
Can you help me to learn more?
(Other definitions for yuppies that I've seen before include "Well-paid middle-class professionals with a lifestyle to match" , "aspirational" , "Young city professionals" , "1980s young and upwardly mobile" , "city careerists" .)