The only civilian sector employers who have anything close to the military's idiotic "up or out" personnel policies are academia, where if you don't get tenure you're out the door, and law firms where if you don't make partner you have to leave. The military isn't exactly a secure occupation, in addition to the hazards of hostile fire zones there are the
problems of training accidents and personnel policies that change with the political winds and whoever's in charge in D.C., plus the downsizing that comes after every major conflict in an attempt to spend the "Peace Dividend". I haven't met too many military retirees who pursued a second career, banked and invested their military pension and became millionaires by age 65.
IIRC one of the reasons for military pensions being established the way they are is the recognition that combat is basically a young man's task, by allowing a fairly early and generous retirement program you will ensure that your military is composed mostly of those young enough to withstand the rigors and strains of warfare.