You can hire a teenager and even a child to take care of your child. Surprisingly, most states have nothing to say about it. Babysitting is outside the realm of much regulation.
The national Department of Labor does not require that child babysitters be paid minimum wage and very few states have babysitting laws. There is also no minimum age requirement in most states, meaning theoretically any kid could watch your kid. So how do you decide when the neighbor's kid really is ready to watch your child?
Guidance From States
Illinois and Maryland are two states that do regulate babysitting, according to Labor of Love. Illinois allows 13-year-olds to work as babysitters. That is an indicator that hiring a babysitter who is at least 13 years old is a good idea.
Some states also have guidelines on how old kids must be before they are left alone -- the recommendations range from age 6 in Kansas to age 14 in Illinois. But note that this is distinct from an age which is okay to babysit (and in Illinois a child may apparently babysit at 13 but that kid's parents may be subject to neglect charges for leaving someone under 14 untended).
As you can see, there is no uniform position on an appropriate age for babysitting or leaving kids alone. Age is just a number, and it does not necessarily indicate a child's maturity.
Guidance From Doctors
The following is guidance from WebMD on deciding whether a preteen child is old enough to stay home alone and to babysit a younger sibling. Watching another kid requires more responsibility than just staying home alone, so make sure that your child babysitter really does have the following qualities, being:
Make sure the child knows how to reach an adult in an emergency and how to contact emergency services. But don't forget to cover the basics, too. Go over everything together the first time you leave the child babysitter with your child:
Make your first outing with a new babysitter short. If it is successful, move on to more. The Red Cross and other organizations offer babysitting certification courses online and in person if it turns out more training is in order.
If a kid understands and can handle your child and house for an hour or two, you are probably safe trying a more extensive adventure next time. Then you can put the little ones to bed and go paint the town red.