"You haven't given me a reason to doubt you." And he did say that he was going to take what Czes said seriously.

"...How long have you been alive?" He couldn't really imagine how it felt to live for eternity, stuck in the form of a young boy no less. The thought suddenly made Steve a little sad. If he was fully immortal, then he would be stuck watching the world change and move on, his friends and family pass on as well.

Steve could barely handle it once, when he lost his era and friends.