The little chap's so late starting! (3)
I believe the answer is:
sol
'the little chap's' is the definition.
'Sol' can be an answer for 'chap's'. I'm not sure about the 'the little' bit.
'so late starting' is the wordplay.
'starting' says to take the initial letters.
The initial letter of 'late' is 'l'.
'so'+'l'='SOL'
Can you help me to learn more?
(Other definitions for sol that I've seen before include "Note, old french coin" , "Fifth note of scale" , "Roman counterpart of Helios" , "Personification of the sun" , "The sun in 12 Across" .)