Betcha they made Chekov 17 in the movie just to piss off the Wesley haters.
I think they did it because making him 13 (which he would've been if they hadn't changed his age) would've been even more
There you go.
It's too bad that they went with the "Muppet Babies" approach to TOS. TOS depicted people of different ages, who graduated with different classes, and had different professional lives before they served on the Enterprise. Now, they'll have been joined at the hip since their early 20s. Why shouldn't Uhura be Captain? She's a clever kid from the same Starfleet class? Or why not genius Chekov? Why should Kirk have command?
It's too bad they chickened out on the hard reboot. We could've just started at year one. Kirk gets his new command. Spock has already been there for eleven years and has been (apparently) passed over for promotion to captain. That's enough for a little tension right there (not the breaking-reason-off-at-the-hinges-suspended-cadet-becomes-captain-in-a-day tension in the 09 film).
Either that, or you really do it Hornblower style if you want to go deeper into the past. We meet Kirk as a Jr. Officer and watch him climbing the ranks, occasionally meeting people who he would serve with later and acquiring a ring of friends (e.g., Mitchell), some of whom could be killed off before he arrives at his first command.