School head still very young! (5)
I believe the answer is:
seven
'young' is the definition.
Both the definition and answer are adjectives. Maybe there's a link between them I don't understand?
'school head still' is the wordplay.
I cannot quite see how this works, but
'school' could be 's' and 's' is found within the answer.
'still' could be 'even' (synonyms) and 'even' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'very' acts as a link.
Can you help me to learn more?
(Other definitions for seven that I've seen before include "Cube root of 343" , "Film" , "Dwarfs or Wonders of the World?" , "Number of Wonders of the World" , "Cardinal" .)