First, his name is "Iron Man" not Carbon Kevlar Man. Second, he is fictional, so Stark is still alive because he doesn't actually exist and can survive things that no real human could. Finally, last I checked, chobham requires backing materials for it to take multiple kinetic rounds. Without that backing, as with other ceramics, it tends to shatter. That backing material adds significant thickness, and the minimum thickness of chobham is usually an inch or more...not really a good material for a mech suit.
...unless you just want Stark to wear a giant cube, but that might limit mobility.
-Nick