GreenKnight121,
I was an active duty Marine for 30 years and was medically retired. I have over 2,800 hours of FMF instructor time in the FMF and more than a passing familiarity with the USMC fixed wing communities and officer corps.
The six years from wings starts from the date of winging. It runs concurrently with other obligations; i.e. the average time to earn wings from commissioning at that time was four years so his six year obligation would have started June of 1993.
On the medical side recurrent vertigo back injuries would have, and in all cases I am familiar with, results in a MOS change if the officer was physically capable of service. In cases where the pilot was bottom line not up to flying in the FMF again a MOS change.
A serious medical problem such as detached retina would preclude the physical requirements of being a cop.
I intimately familiar with cases where an officer stepped all over his d*** with golf spikes and was allowed to resign for the good of the service and other reasons being given, the most (in)famous being a general officer.
For the record I am not a Brit.
S/F FOG