This isn't about canon.
It's a question of who is a slacker and who is criminally complacent.
Driver, and character.
Picard was a captain at 27... Over his Captains dead body, side stepping advance and promotions, he just said "I'm captain, anyone got a problem with that?"
Riker was XO of the Flagship by 27, but he probably had a lot of skull and bones backing him up from Pressman and the Pegasus.
Kirk was captain by 30, but he had Robert April guiding his career.
Could Kathryn get into trouble for not promoting people enough?