Well, they mucked around with Chekov's age (but then, given his swiping of Spock's human calculator schtick, I'd argue NuChekov is, along with NuScotty, much closer to a different character than the rest). Figure that NuKirk et al are at best early 20s, where previously Kirk would've been more like 30 when he became Enterprise captain. NuChekov is several years closer in age to NuKirk than the originals were.