The cashier could be anywhere from 19 to 22 years old, I guess. Suppose she graduated and started working, then the humdrum of the work force could have gotten her within a year.
Although the artwork is really rough, I think it benefits from being consistent in the way characters and facial expressions are done. Their depictions are simple, but you can pick up the vibes and there are no slip-ups. It's kind of like Ratana Satis' immaculate anatomy, just... erm, in a simplistic way.