Asuna's more or less the timeless wife type now. Boring? Arguably.. Still prolly the best one for a long term relationship though.

As for asking a "highschooler", well they're asking the guy who broke through the biggest death game in their industry. I don't see any discrepancy there. He's good enough to become their mole and is also skilled enough to detect a cheat/exploit when he sees one (remember Kayaba's impossibly fast moves?). Anybody who's watched this show till now shouldn't be surprised nor be perplexed as to why Kirito was called upon, especially anybody who's ever called him a Mary Sue.

I hope SAO really ends up being the prequel to Accel World and not just some related universe with a similar idea. Kuroyuki needs to be Kirito's daughter.