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'm not sure about the 'quite' bit.
'so advanced' is the wordplay.
'advanced' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'so'+'on'='SOON'
'to be' is the 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" .)