To have fun with this, you need to start young (3)
I believe the answer is:
toy
'to have fun with this' is the definition.
The definition suggests a singular noun which matches the answer.
'to start young' is the wordplay.
'start' suggests taking the first letters.
The first letter of 'young' is 'y'.
'to'+'y'='TOY'
'you need' acts as a link.
Can you help me to learn more?
(Other definitions for toy that I've seen before include "One of spelt out words" , "Miniature (dog)" , "Trifle or dally with" , "Small breed" , "Child's amusement" .)