Its supported by a general body of knowledge regarding behavioral patterns in humans. Barring losing his marbles for one reason or another, behavior patterns and world perspective dont change in most people after early 20's let alone 60's or 70's.

While it is also possible he just simply cracked for one reason or another, it seems like it must have happened a while ago.

As far as retirement age, I did not see a number. Many people retire when they can take SS, however it is possible in his case he retired around 50 if he joined up at 20 or so and had a 30 year pension.

His response to the incident seemed lucid enough, and he tried to articulate a defense of his actions. One that actually would have flown more likely than not was he still wearing blue. Or in other words, his post-incident behavior and demeanor fits my model much more closely than yours. Your "justification" is just a rhetorical hand-wave for things you dont want to consider.

Of course it is also possible, and even likely that a combination of the two factors (worldview + marble lossage) was at work. This I would accept as reasonable, its entirely possible that a decade ago he would have been a codgety old intimidating asshat, but had enough self control not to up and shoot someone for little reason.

For who could be free when every other man's humour might domineer over him? - John Locke (2nd Treatise, sect 57)