The Deadly Years - Kirk states that he is 34 years old.
Who Mourns for Adonais - Chekov states that he is 22 years old.
Cut to: The bridge where Captain Pike asks the “Russian whizkid” at the helm what his name is. It’s Ensign Chekov. Cue a comedy sequence where Chekov attempts to enter an authorization code into the computer, announcing “nine, five, wictor, wictor, two” in a perfect Walther Koenig exaggerated Russian accent and being denied. Chekov goes on to address the ship over the comm., stating that anomaly has been detected in the neutral zone, a lightning storm in space. A distress signal from the Vulcan (“wulcan”) high command has caused the Enterprise to go and investigate.
This was my concern with using all seven characters in a Kirk origin tale. It makes no sense that a character that is twelve years younger than Kirk already being a bridge officer.
Not to mention the fact that evidenty the Enterprise is only three years old when Kirk first shows up. Definitely steals some of the non-canon thunder from the Chris Pike. Plus, poor Robert April no longer exists.
And while that is true, something like someone's age is never really THAT important, and I'm sure 99% of the audience who see the movie will have no clue that Chekov should only be 22.