Quite early to be so advanced (4)
I believe the answer is:
soon
'quite early' is the definition.
'soon' can be an answer for 'early' (I've seen this before). I am not sure about the 'quite' bit.
'so advanced' is the wordplay.
'advanced' becomes 'on' (I can't justify this - if you can you should believe this answer much more).
'so'+'on'='SOON'
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for soon that I've seen before include "Before long" , "Before you can say Jack Robinson" , "In the near future" , "Early, in a short time" , "Willingly" .)