Whizz kid's very curious message, never opened (2-6)
I believe the answer is:
go-getter
'whizz kid's' is the definition.
(both can mean a talented person)
I don't understand how the rest of the clue works.
(Other definitions for go-getter that I've seen before include "Informally, an agressive achiever" , "Thrusting, ambitious type" , "Enterprising person" , "One who succeeds through energy and drive" , "Someone whose career progresses rapidly" .)