My daughter pet sits for many people in our neighborhood. She will be 16 next month and has been doing this for about 4 years. Up until this year, she wanted to be a vet. She absolutely loves animals and they love her. We even had one owner say to us, while standing in her driveway, that her cat will not go to anyone but her and her son. Well, she no sooner got done finishing her sentence than the cat was letting my daughter pet it. When she was little, we went for walks thru the neighborhood and all the cats would come out of their hiding places to see her. Needless to say we never got our heart rates up!
We have one neighbor who has moved (about 5 minutes away) and they still call my daughter to dog sit. We know the garage codes for many people in our neighborhood, but people trust us with their homes and with their pets. (My husband or I always go with her. I would never send her into an empty house.) We always make sure we have emergency info. Once we went into a house where there was a gas leak! Scary! My daughter lets the customer decide what to pay her. So far only one was a cheapskate (expected her to dogsit for free since it was only one night), and she doesn't dogsit for them anymore. Her customers want to keep her happy, so they make sure they pay her well. Some will even bring her a gift back from a vacation in addition to paying her. She not only feeds the animals, she spends considerable time playing with them.
My point with all this is that neighbors -- including young teens -- can be good petsitters. My daughter's "business" is by word of mouth from those she has "worked" for. Obviously she is very mature and an animal lover. My advice is to ask around and you may find someone you can depend on. Even if they come every other day for the cats, if they spend some time with them, the cats should be fine.
Good luck.