And, teenage drama isn't quite exactly the definition of a mature show.

• The tone of the new series is older. The main characters are in their late teens, with Korra herself being 16 or 17.

If that's what you mean, it's talking about the characters being older and it's mostly paraphrasing from AS.net's part.

Are you looking to win new viewers with the series or just satisfy fans of the old series who have grown up?

DiMartino:We want everyone to watch. Definitely fans of the first series will not be disappointed in this one. The tone is a little older, the characters are a little older than the first series—they're teenagers. Korra is 16 so she's older than Aang was. So I think maybe some people who weren't into the first show might find this one and be into it.

and of course

Since the main characters are older, will there be more romance?

Bryan Konietzko:I thought Korra was 17 so Mike and I have to get our stories straight. The main characters are in their late teens, we've always loved those kind of teen love triangle type stories and there was plenty of that in the original series. We're definitely getting into it in this series. The difference is these people have cars and motorcycles and things. There's definitely a different dynamic. I'd say the show is more sophisticated than the original series but it has the same balance of tones we've always liked with humor, action, drama, scary stuff and romance.

So. Yeah. Nothing on it being "more mature" a slightly older tone since the characters are a bit older, and the series being more sophisticated while still having the balance of tones like in the past series, that's all there is.