You put too much weight on senility as opposed to early-onset age related conservatism.
Then why did you use the term senility instead of "conservatism"? And why does that conservatism mirror the attitudes among the junior leadership of the time as well?
My underlying calculation:
~1920-1925: Start of problems of colonial system (lowering productivity and profit margin, resistance to external rulers)
~1933: US, as fastest-loop state of epoch, starts acting on issue (Good Neighbour Policy, planning of Philippine independence)
~1946: Medium-senility states (British) realize the problem too
~1955: Even senile Japan realize the colonies are hindrance rather than any benefit
And where does France, whose attempts to hold onto it's colonies almost led to a civil war in the 60's, fall under that?
They were backed into a corner. The US demands on Japan were impossible to meet without the collapse of Japanese politically.
FDR was determined to force Japan into a war.
https://mises.org/library/how-us-economic-warfare-provoked-japans-attack-pearl-harbor
And the Japanese ensured he would not only get his war, but also sustain it for the long haul. Even if we assume that the Japanese were wedded to war and accepting American terms and giving up on the hemorrhaging ulcer that was China was not the
truly smart thing to do, the way the Japanese went about in getting their war was blatantly suicidal and eliminated even the smallest chance of success. Above all: Yamamomoto's obsession over hitting Pearl Harbor, which was both operationally unnecessary and strategically disastrous yet so popular with the IJN that he managed to bully his Admiral Nagano into accepting it. Nagano's own plan is generally accepted to have been far superior... which is unsurprising since he, and not Yamamoto, was supposed to be in charge of strategic planning! If the US
did intervene against the strike south, the USN would have been forced to fight a war on the other side of the Pacific at the end of very extended supply lines, using a base (the Philippines) that in 1941 was totally inadequate to support a large fleet. This would draw poorly supplied American forces into Japan's back yard in a war of choice while the Japanese would be close to their own logistics hubs, with shorter internal lines of communication, and a more compact and easily defensible perimeter.
If, on the other hand, the USN stuck to what it's warplans called for and sat back in the East Pacific for two years while building up it's logistical strength, then the inaction could sap at American political will which lacks the same sort of stamina that the rallying cry of "Remember Pearl Harbor!" provided.
Under either such circumstances, Japan had the chance of winning some early victories, which in turn at least held out the
hope of leading to a negotiated settlement to what in America might be an unpopular war. The odds were still long and something like the Bataan Death March could still occur which would have driven US outrage to similar heights in Pearl Harbour's place, but there was at least there was a
small chance of success. In comparison, Pearl Harbor was nothing more than a suicide pact.