There had been a time, whenever there was a slow second in their lives (rarely) and Tony had run out of ways to make their conversation about himself (which was, Tony was tired of Nick berating him for his more than fair share of character defects), that Tony could be counted on to demand how Nick was so fucking young. That probably wasn't the way he had first put it, because at 18 years old Nick had seemed ancient no matter how Tony looked at it, but that was really the question he was asking. Why don't you retire, old man? Maybe let me take over, because I know everything.
That was a long time ago, before Tony realized that if he was going to get anywhere, he had to keep on learning. And what he quietly learned, and that Nick didn't need to know, was that Nick definitely wasn't a mutant. Tony knew what was in his blood and had a still incomplete database of other men involved in the project. But Tony's head rolled on the subway platform floor, hair starting to curl in th heat gray with the dust and dirt that could only partially be blamed on the explosion, so he could grin at Nick through his finale like he was glad to finally be let in on the secret.
Most of Billy's story wasn't new to Tony either, though he snickered immediately at Ass Guardian, throwing Billy a baffled glance for ever thinking that was a good idea-- and only after he had laughed did he realize Billy had intended Asgardian. It couldn't be helped, Billy didn't come off much like the mighty God of Thunder or any of his powerful pals. Then Tony had to laugh more.
When he'd calmed down enough, he was looking at Nick again, wondering how he should give his own answer. He could leave them with the story they already knew, but Nick probably deserved to hear the rest of it-- the actual reason Iron Man was a hero. He said, "I made something incredible so that I wouldn't die. When I made it I thought it was so I could go on doing the same thing-- living the same way. I was going to produce a million of them. I was going to marry the girl who had waited for me when everyone thought I was dead. But when she saw the suit, and saw how people reacted to it, and who I could have been, she left me. She told me to paint it gold." Tony was staring up at the rocks suspended above them again, like he could see Joanna the way he had conjured that image of Steve for himself, but when he finished speaking he looked to Nick again hoping that was enough of an explanation for him.
His question, when he had rolled his head back to glance at Billy and make sure they were all on the same page, followed naturally to Tony. He asked, "What would you give it up for?"