Getting on in the Runaway Train's destination (4,3,4)
I believe the answer is:
over-the-hill
'getting on' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for over-the-hill that I've seen before include "No longer at ones' best" , "Elderly" , "Past one's best" .)