One of many youngsters certain to pinch pennies ahead of rising rent (9)
I believe the answer is:
septuplet
'one of many youngsters certain' is the definition.
I can't judge whether this definition defines the answer.
'pinch pennies ahead of rising rent' is the wordplay.
'pinch pennies' becomes 'sept' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'rising' becomes 'up' (similar in meaning).
'rent' becomes 'let' (I've seen this in another clue).
'sept'+'up'+'let'='SEPTUPLET'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for septuplet that I've seen before include "unusual baby" , "One in large family" , "Quick notes" .)