Clint takes this in, the idea of long lives, better physically, the idea of specialness bestowed on certain people. Like Loki, he guesses. And Thor. And so on.

"Would anyone even want me here? An outsider who's not gonna live so long and who doesn't have super senses? Besides Loki, I mean. I don't exactly fit in." In any sense. Does he fit in back on Earth-Midgard? Not really either. So what exactly does it matter?