Clearly they're making him look older and "more mature" in the official photographs, because they reckon that's going to increase his mainstream credibility.
I think the main point isn't so much that he *looks* different in Grace Kelly, but that, apart from all the lighting effects, he's giving off a different vibe. In his interviews and public performances he's very kid-like, but sometimes when he performs he gets more serious and focused, he's got this different "persona". I think that's a conscious choice, since he says he was involved in almost every aspect of the making of the video, and he thought that that attitude would be the ideal manner in which to channel the feeling of the song.
Most people have a different vibe in their performance than in real life.
He's hot either way, mind.