This is pre Kazuma. So Aqua will be the one to greet you, however since this is before Kazuma you can do either choice, or make your own.

Here are the choices

A. You know of Kazuma and warn Aqua in advance.

B. Make the same choices Kazuma did, leaving Kazuma to Goddess Eris.

C. You make your own choice.

Also, since Aqua's wiki states she ageless. She will be over Four thousand years old, but will keep her appearance so in short, Four thousand years old with a the appearance of a twenty-four year old body. And if anyone is wondering, no Megumin will not appear, Darkness however yes.

And on a side note, everyone else that had bumped into will be over 18 as well. But that's for you to decide if they appear or not. They could just be small cameos.