Perhaps glass ceiling: no opening for job with old head of company at its core (8)
I believe the answer is:
obstacle
'perhaps glass ceiling' is the definition.
(I know that glass ceiling is a obstacle)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for obstacle that I've seen before include "stumbling block" , "Stab Cleo (anag) - which hinders progress" , "Thing blocking progress" , "Block to progress" , "It obstructs or hinders" .)