Short answers, pulled from the story.
General is the highest commissioned officer rank ordinarily attainable in the United States Army, Marine Corps, Air Force, and Space Force, designated by four silver stars and pay grade O-10. It ranks above lieutenant general (three stars) and below the five-star grades of General of the Army and General of the Air Force, which are reserved for wartime use.
Statute caps four-star officers at eight Army generals, nine Air Force generals, two Marine Corps generals, two Space Force generals, six Navy admirals, and two Coast Guard admirals. Additional four-star slots exist for positions such as chairman and vice chairman of the Joint Chiefs of Staff and commanders of Unified Combatant Commands.
The president nominates candidates from eligible officers holding the rank of brigadier general or above, acting with advice from the secretary of defense, the relevant service secretary, and the Joint Chiefs of Staff. The United States Senate must confirm the appointment before the officer can assume the rank.
Most four-star generals serve a standard two-year tour, renewable by renomination; service chiefs and the chairman and vice chairman of the Joint Chiefs of Staff normally serve a single four-year term. Upon retirement, officers are typically nominated to retain the four-star grade rather than reverting to the permanent two-star rank of major general.
All general officers must retire the month after their 64th birthday unless granted an extension. The secretary of defense can defer retirement to age 66, and the president can extend it further to age 68. A general who wants to retire at four-star grade must have at least three years of satisfactory active duty service in that grade, certified by the secretary of defense.
General and admiral are equivalent four-star grades, with general used in the Army, Marine Corps, Air Force, and Space Force, and admiral used in the Navy and Coast Guard. Both are O-10 pay grade and are subject to equivalent statutory caps and appointment procedures.