Highly valued clothing company is strikingly advanced (10)
I believe the answer is:
precocious
'strikingly advanced' is the definition.
'highly valued clothing company' is the wordplay.
'highly valued' becomes 'precious'.
'clothing' is an insertion indicator.
'company' becomes 'co' (abbreviation).
'precious' placed around 'co' is 'PRECOCIOUS'.
'is' is the link.
(Other definitions for precocious that I've seen before include "early talent" , "Early in developing" , "Developing earlier than normal" , "Advanced" , "Mature beyond years" .)