Return part of Jubilee line seems unsteady and old, perhaps (6)
I believe the answer is:
senile
'unsteady and old perhaps' is the definition.
'return part of jubilee line seems' is the wordplay.
'return' is a reversal indicator.
'part of' indicates a hidden word.
'elines' is hidden in the letters of 'jubilee line seems'.
'elines' written backwards gives 'SENILE'.
(Other definitions for senile that I've seen before include "Suffering infirmities of old age" , "Suffering from ailments of old age" , "Suffering from old age's weaknesses" , "Mentally weak due to old age" , "Mentally infirm with age" .)