FanFest revealed that their lifespans are a little longer than the other Spoken races, and thus age a little slower. I'd only put them delayed by a few years. I'd put the Elezen characters we can make at mid twenties, while most other races are likely late teens-early twenties. To start, anyway, as you can use faces that look older.

So in the grand scheme of things, it's no surprise that Alphie had the wool pulled over his eyes. He's still a kid in the eyes of Eorzea. Granted, he's got quite a legacy to live up to, but he's still a kid, more or less.