I was well aware (from movies and TV series) that at 15 years of age boys and girls can already drive here in the United States, albeit with an adult on the passenger seat, and that at 16 years old they are ready to get behind the wheel on their own, yet I was surprised to see young teens driving once I moved here.
Back in Italy, you can start training for driving at 17 years of age but only with a driving school.
After some lessons, if you are skilled enough, the driving school and the Department of Motor Vehicles will issue a sort of temporary license you can use to train side by side with an adult.

I think the culture here is very different for many reasons.
First of all, these kids leave school around 2 in the afternoon and after that, many teens go straight to work, even on Saturdays and Sundays. Then, they have to rush home to study and go to bed early, because high school classes start between 7 and 7.30 in the morning.
In addition to that, they often have extra-curricular activities: sports, choir or music.
In short, they are very busy and leading such a busy lifestyle requires them to have a car and be independent as soon as legally possible, also given the large distances in the States and especially here in Texas!
Unless one of their parents has nothing to do, chauffeuring these kids, far and wide, around the city, is not an easy thing. Sometimes, parents carpool, meaning that one parent takes several kids at a time and the families take turns doing it. Hence, it is easier for everyone to make them autonomous as soon as possible. Thanks to the ease of driving the car with automatic transmission and the tranquility with which Americans drive, getting a license becomes quite simple. I don't think I would be so relaxed in a metropolis to have teens driving around but here in Texas the roads are really wide and mostly straight so it’s a piece of cake!
Kids can actually begin as early as 15 years old to prepare for their knowledge test and they can start studying at 14 years old the study manual that can also be found online on the Department of Motor Vehicle website.
The knowledge test is supported through a terminal with multiple choice questions and it is offered in several languages given the large immigrant population of the States.
Some are tricky questions, where the words can be misleading, but with a little common sense it is really trivial.
I had to pass it too to convert my license once I got here.
Once they have taken the theory test, and if they are at least 15 and a half years old, they are authorized to begin practicing after they pass an eye examination.
A driving school normally offers packages including theoretical lessons in the classroom, driving time with an instructor, a car for the students to use if they don’t have their own family one.
As for car insurance for kids under 18, the costs are high but, by providing a good school report card every six months, they get cheaper because a boy or girl who is doing well in school is considered more conscientious to drive.

I wanted also to mention that on the American driver’s license they include information like the weight and height of the driver which was a surprise to me coming from Italy.
On your driver’s license you can also mention if you are an organ donor or not, in case of an accident.