Condition guarantees pain for someone getting on (14)
I believe the answer is:
septuagenarian
'someone getting on' is the definition.
(someone in their seventies - 'getting on' is aging)
'condition guarantees pain' is the wordplay.
'condition' indicates anagramming the letters (I've seen 'conditions' mean this (letters must be in a new condition)).
'guarantees'+'pain'='guaranteespain'
'guaranteespain' with letters rearranged gives 'SEPTUAGENARIAN'.
'for' acts as a link.
(Other definitions for septuagenarian that I've seen before include "Elderly person" , "OAP" , "pensioner" , "One aged 70 to 79" .)