@Roger Rambo:
Even the rendered scenes can be somewhat contradicting. I mean, when the Chief linked up with Lasky and Palmer's party after the Infinity's crash-landing, Palmer told him "I thought you'd be taller". In that scene, the height difference isn't as noticeable as in the Legendary Ending's final cutscene.
Of course, Palmer's comment could be interpreted as a (wry) joke.
And, yes, I know that scene was rendered by the game engine (or so it seems to me) as opposed to pre-rendered CGI for the LE cutscene and, therefore, proportions will be inconsistent because 343 used different 3D models for either cinematic.
As for MC's wrinkles...
Don't forget it's a close-up and wrinkles
will therefore be more noticeable. On top of that, Spartan-IIs, even early in the Humanity-Covenant war, already sported a nice collection of scars, due to either intensive training and active combat (anti-insurgency warfare). In FUD's last episode, you can clearly see that both Fred and Kelly already had a couple of scars on their heads/faces.
In H4's legendary ending cutscene, the Chief has two scars around his left eye, one on his eyebrow and one on his cheekbone. There might be one on the right side, but it could be a visual trick caused by the camera's angle.
As for the rest, well...you could chalk it up to lack of sleep. I mean, he only rests when he gets knocked out - otherwise he's continuously peppering the landscape with ammunition. C'mon, can't you see those dark circles around his eyes? J/K
P.S. Yes, I know there is a theory making the rounds, according to which his dark eyes are