Quite honestly, when i read this all ...
Im surprised someone presume they shouldnt be level 1.

You quite literally gave us your take on why they have level 1

It's not explained in game so far so we all make up our own reasons why people who have been around some time are at level 1 because logically speaking, as someone already stated, killing rats should give you at least some experience. And yes, once agaian, I realize it's a game mechanic but we do what we gotta do to put the story 'right' in our heads

Harmless fun.