Its fairly common knowledge he isnt as professional in some areas as he could be. Turning up late for training for example. Using his age as an excuse is a cop out imo. He's in his 4th year of first grade, with some of the best nutritionists and some very, very good professionals around him at the Broncos. He knows what he should be doing, he's got plenty of people pointing him in the right direction.
At the moment, i think his fitness is fine. I think he's lost a little explosiveness in his speed with him bulking up a little, but if he's not careful i could see him certainly carrying a bit too much weight. My issue with him last night was him going to close to the line in wet weather. It was dumb, everyone who knows slightly anything about the game knows doing that on a slippery surface is a bad idea.