You are mistaken. You can serve in the US military at age 17. They are generally avoiding it, but legally it can happen. They are not allowed to send soldiers under age 18 to war zones, but sometimes the war zone comes to the US military.
I really have to ask at this point: did you serve? You do not seem to know much about it.
Most states have a learners permit at age 15, and a license at age 16.
Correct, one can join at 17, need parents permission.
Had a motorcycle license at 14, but limited in size of bike. I know because I worked a job at that age and rode to work every day, had a 250cc Kawasaki.