Legally only of minor importance (5,3)
I believe the answer is:
under age
This could be a double definition.
'legally only of' is the first definition.
The definition suggests a singular noun which matches the answer.
'minor importance' is the second definition.
The definition suggests a singular noun which matches the answer.
Can you help me to learn more?
(Other definitions for under age that I've seen before include "Like a minor" , "Too young" , "Immature" , "less than 18?" .)