2517-2519 John is recruited/stolen at 6 and in 2 years made squad leader

2525 First Contact... not good for Harvest, got to see Johnson kick some ass though

2552 AUG 30- Reach happens... Spartan suicide, well for those that survived training, augmentation, the civil war amongst the colonies, IE the reason Spartans were created to fight rebels with little collateral damage to UNSC forces... or so ONI says...

2552 Sep 19-Sep 22- Halo CE happened and was over... only 7 lived

2552 Oct 20ish- Halo 2 starts with Arbiter scene ends with New Membasa getting owned, ODST starts right after slip space rupture, ends within a week

2552 Dec 9- Master Chief bails and falls to Earth, Halo 3

2552 Nov-2553 March- entirety of Halo 3 plays out

2553 March 3- the hill side scene ends with both peace and Halo Legendary ending... my money's on the legendary connection to the shield world at Onix

Master Chief is at least 42, not counting any cryo sleep that affects physical age, the Cov/Human war has been going on for 28 years, if ONI records are correct... considering they fucked up all of Halo's timeline with UNSC propaganda bullshit... like Spartans never die they just go MIA