For those pilots who have been involved in training, there are far more options available be it MCC or SFI etc.
CRM ground school available for those who enjoy pontification usually with a gift of the gab.
Light ac flying as a FI would keep you busy. There is a desperate shortage of experienced pilots.
ATCOs in "retirement" often end up at FTEJEREZ at the ATC training school.
A cautionary note: attempting to start training ( as an instructor EASA SFI qualification ) for the first time at retirement age has / can prove to be unsuccessful. An expensive car crash.
Something about old dogs and new tricks springs to mind.....?