Speed of progress through life (6)
I believe the answer is:
career
I believe this is a double definition.
'speed' is the first definition.
(I've seen this before)
'progress through life' is the second definition.
(I've seen this before)
'of' acts as a link.
(Other definitions for career that I've seen before include "One's life's work" , "Mad rush" , "Run wildly" , "Move rapidly in progress through life" , "Progress through profession" .)