[Faralen]

Dubs are usually terrible. I am convinced it is because non-Japanese (or at least most) voice actors fail to take the acting seriously. The characters almost always sound younger in dubs. This isn't always true though, since some anime (like Cowboy Bebop) have amazing dubs.

I would certainly hope Asuna and Kirito wouldn't sound older. When SAO began they were 12/13 or was it 13/14? So they are young, puberty hasn't kicked in. Though Asuna's voice sounds too young in my opinion, Kirito's is perfectly fine. I normally stay away from dubbed versions, Code Geass being an exemplary exception. One anime I can see being ight with a dub is Highschool of the Dead, I watched it subbed and it seemed to take it all too seriously, whereas I hear the dub was more relaxed, and more comical. Which is nice cause the anime sucked, and was more comical.

Cowboy Bebop has a good dub? Might have to watch it dubbed when I get around to it ^-^

Not sure when puberty kicked in for you, but for me it was around 13, Kirito was 14 at the start of the Aincrad arc and Asuna was 15.

http://swordartonline.wikia.com/wiki/Kirito
http://swordartonline.wikia.com/wiki/Asuna