Agree, it was certainly unexpected by me and many others I'm sure. Was blown away at how well he did and more importantly his presence made basically the whole OL better as a whole. Definitely a promising player and I can only see him improving.
As for maturity, speaking for myself I didn't see much of an issue. I love his intensity, toughness, and the way he sticks up for team mates. He fits right in with Allen, Diggs etc with his sense of humor and having fun.