If you've been following recent events in the Attack on Titan manga, you'll have seen that it seems to be validating some originally far-fetched sounding theories based on No Regrets, Birth of Levi spin-off manga. Probably related to this, there's been talk about Levi's age. Enough talk that the manga author has decided to comment on how old the popular character is.
そういえば、リヴァイが30歳との噂が回ってるらしいですね。諫山さんにも確認しましたが「30歳よりは上だけど、今後の話に関わる可能性もあるので具体的には言えません」とのことでした。— 「進撃の巨人」担当者バック (@ShingekiKyojin) August 14, 2014
From the official Twitter account:
"There is a rumor that says Levi is 30 years old. I checked and Isayama sensei said Levi is older than 30, but would not go into details because it may be related to the yet untold story."