How petty. Can't help out the local community without being accused of having an ulterior motive, huh. Especially since it involves delicious food for a change, something these two in particular must have missed a lot. He should've brought his bro or come alone.
They are just high school kids, at the end of the day. While dying and getting isekaied, and then having to take care of themselves 100% in a strange, more dangerous world should mature a person more rapidly, it would also strip away some of the modern politeness and manners, so they would be cracking harsher jokes more freely. We have seen this kind of behavior and talk before.
They are high schoolers so around 16, Aera just looked young but her age probably near 25. In this world, elves are not immortal, they just have slightly longer lifespan.
Twice as long. If physically growing up is slower, Aera might not even be fully grown up. Her circumstances might have been somewhat extraordinary for her to open a shop, alone, in a human town. But then again, maybe you are correct and she's just an eternal loli.