Mature pier design, to a point (5)
I believe the answer is:
ripen
'mature' is the definition.
(to ripen is to mature)
'pier design to a point' is the wordplay.
'design' indicates anagramming the letters.
'to a point' becomes 'n' (N is an example).
'pier' anagrammed gives 'ripe'.
'ripe'+'n'='RIPEN'
(Other definitions for ripen that I've seen before include "Become mature" , "Develop fully" , "Become ready for picking" , "Grow older" , "Get ready to open" .)