As has been stated, there are 51 different sets of laws for the age and restrictions on drivers. Most states have 16 as the minimum...but I've known states allowing "permits" (where you can drive on the road with a licensed adult for educational purposes) that allowed drivers to be as young as 14 (South Carolina did this until a few years ago). Some states are raising this level now and 18 seems to be the goal for a full license.
Driving with passengers, again, is on a state-by-state basis.
Pennsylvania (a few years ago...this is changing now) allowed for a "permit" at 16 (and not a day before). At any time, the driver could take the behind-the-wheel test and get a "Junior" license, which allowed for driving between 6am and midnight. At 17 and with proper documented education, you could apply for a "Senior" license, which would allow for unrestricted driving. Automatically, at 18, a Junior license would become a Senior license.