Justin looked a lot older before he got famous if you see any of his Youtube clips. They just cleaned him up with Proactive and gave him a kiddo haircut so that he can appeal to the tween market and sell a lot of shit. Music companies have been doing that for decades. Once they finish clearing out the kiddie market, they turn him up for an older demographic to take their money and so on.
Take Aaron Carter for example. Looked like he was 12 years old for years. After they finished with him......

He'll look like a 12 year old until the music company saturates the tween market. Then that will be that.