It does hold together well, but how much of it was actually seen onscreen?
A fair amount actually. I'll add some comments.
Maybe this will help ...
2249 - Age 17 - With the backing of Commodore Mallory, James T. Kirk, second son of the late Commander George Kirk, enters Starfleet Academy at the youngest age allowed. 1.
2253 - Age 21 - Kirk graduates from SFA, is commissioned an Ensign and posted to the USS Republic an older light cruiser commanded by Capt. Garrovick. 2.
2254 - Age 22 - Republic is damaged and sent back to Earth for repairs Capt Garrovick is transferred to the USS Farragut Constitution class heavy cruiser whose skipper was killed on a mission, he takes several officers with him as crew replacements including Kirk. Later Kirk is promoted to Lt. jg and acts as Garrovick’s aide at the Axanar Peace Mission. 2.
2255 - Age 23 - Farragut is attacked by the cloud creature at Tychos IV, half the crew, including Captain Garrovick, is killed, Kirk helps bring the crippled ship into port. Kirk is nominated to Command School and travels back to Earth to begin the curriculum. 3.
2256 - Age 24 - Kirk is re-united with an old friend: Gary Mitchell, an upperclassman in the history class he teaches. Kirk beats the Kobayashi Maru scenario, he is awarded a commendation for ‘original thinking’ and promoted to full Lt. He also becomes involved with Carol Marcus at this time. 4.
2257 - Age 25 - Kirk graduates from Command School with high honors, he is assigned as Navigation Officer aboard the USS El Dorado a light cruiser commanded by Capt. Stone. 5.
2259 - Age 27 - Kirk is promoted to Lt. Cmdr. and transferred to the heavy cruiser USS Constitution as Executive Officer under Capt. Rexar Vetra of Andor.
2260 - Age 28 - Kirk takes command after the Captain is killed during an engagement with a Klingon cruiser and 3 destroyers, he evades then re-engages crippling 2 of the destroyers, damaging the cruiser and forcing a Klingon withdrawal. He is awarded the Medal of Honor, Karagite Order of Heroism and a Starfleet Combat Command Star. Upon his return to Earth Kirk is posted to his first command the older light destroyer USS Ariel, he requests Lt. jg Gary Mitchell as navigator. 6.
2261 - Age 29 – Kirk’s on again - off again romance with Carol Marcus results in a son. At Carol’s request Kirk distances himself from them. 7.
2262 - Age 30 - Kirk is promoted to Commander and posted to the heavy frigate USS Lydia Sutherland, here he first meets the irascible Lt. Leonard McCoy MD. 8.
2263 - Age 31 - Kirk and Lydia Sutherland protect the Arulia outpost from a Tholian swarm. Alone they hold on for 97 hours before reinforcements arrive. Kirk is awarded the Star of Valor and promoted to Captain. 9.
2264 - Age 32 - Kirk is assigned to command the USS Enterprise, the handpicked successor of Fleet Captain Christopher Pike. Undertakes mission to the galaxy’s edge. 10.
2265 - Age 33 – Kirk begins five-year mission of exploration aboard the Enterprise.
The details, like ship names and so forth, can be argued. But it holds together fairly well.
1.) Mallory helped Kirk into the academy (The Apple), Kirk entered the academy at 17, father dead (backstory from the Writer's Guide)
2.) Kirk served on the Republic as an Ensign (Court Martial) Kirk served as a Lieutenant on the Farragut, Farragut was commanded by Garrovick, Garrovick was Kirk's CO from the day he left the Academy (Obsession) Deduction - Garrovick had also been CO of the Republic.
3.) Kirk helped bring the Farragut in (Obsession) Most officers don't attend Command School until they have had a few years of active duty (real world practice)
4.) Kirk taught as a Lieutenant at the Academy, Mitchell was one of his students (WNMHGB) Officers in command school frequently teach lowerclassmen as part of their duties. (real world practice) Mitchell set Kirk up with a girl that he almost married, presumed to be Carol Marcus (WNMHGB)
5.) Kirk had been a navigator ten years ago (The Corbomite Manuever) Kirk and Commo Stone clearly knew each other, with Stone as the senior, Stone had been a starship captain (Court Martial)
6.) Kirk had the Medal of Honor and Karagite Order of Heroism (Court Martial) Kirk's first command was a destroyer class spaceship (writer's guide) Asked for Mitchell in his first command (WNMHGB)
7.) all established in TWOK
8.) McCoy and Kirk had clearly known each other for a while and had probably served together before. This seemed like a good spot to add him.
9.) Kirk had to do something spectacular to get command of one of the 12 so young. This is what I came up with. Could be swapped out with a better idea.
10.) Every one of the Constitution class captains is going to be hand picked. These are the best of the best. Mission to galaxy's edge from WNMHGB.