In the comics, the suggested material is iron/steel and the only material close to such property is titanium alloys.

That was definitely the case when Stark made the first suit. But later incarnations probably don't have steel in them, they are almost like some kind of nano thing.

However, putting nuclear power in the suit that a human is going to wear is not a good idea unless the human is Hulk.

😄

So I guess, at least where flight is concerned, there can be no Iron Man in real life. But then, maybe that's just because there's no Toni Stark in real life!