<Li> The Assistant Commandant of the Marine Corps serves for two years . </Li> <Li> The Chief of the National Guard Bureau serves a nominal four years . </Li> <P> Extensions of the standard tour length can be approved, within statutory limits, by their respective service secretaries, the Secretary of Defense, the President, or Congress but these are rare, as they block other officers from being promoted . Some statutory limits can be waived in times of national emergency or war . </P> <P> Other than voluntary retirement, statute sets a number of mandates for retirement . A four - star general must retire after 40 years of service unless he or she is reappointed to serve longer . Otherwise all general officers must retire the month after their 64th birthday . However, the Secretary of Defense can defer a four - star officer's retirement until the officer's 66th birthday and the President can defer it until the officer's 68th birthday . </P>

How do you earn stars as a general