Feed supporter - that's immature (11)
I believe the answer is:
caterpillar
'immature' is the definition.
Both the definition and answer are adjectives. Maybe there's a link between them I don't understand?
'feed supporter' is the wordplay.
I cannot quite see how this works, but
'supporter' could be 'pillar' (pillar is a kind of supporter) and 'pillar' is located in the answer.
The remaining letters 'cater' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for caterpillar that I've seen before include "crawler" , "Butterfly/moth larva" , "Tiny creature" , "looper, perhaps" , "He made do with a mushroom" .)