Aziraphale just smiled. "You asked," he said, with a little shrug. After all, if he was concerned about humans believing him, then he wouldn't have made it very far in their world. That was actually part of what made it easy to pass unnoticed; even if he did say something strange, it was unbelievable enough that it was readily dismissed.

"How old are you?" he asked, politely, because he figured it would be fair to ask in return.