I'm going to agree with the ones saying it's mostly suit mass, not the user being a little lower on the fitness scale.
Because when you think about it, the Nanosuit and Nanosuit 2 are big, bulky exoskeletons that have to store all the tech and hardware externally and provide full-body protection.
And considering that "bulk" holds the ability to toss cars, stop bullets, and numerous other extreme feats, it's bound to be big. And you have to keep in mind that the original Nanosuit was an "inferior" model than the newer, more powerful one.
From what I've seen of it, the suit looks pretty good.