That part varies from state to state, as well as what relation you have to have with that person; in some states, they have to be a parrent or guardian, in others they don't care.
Here in florida you have to have some 21 or older in the passenger seat with a valid full drivers license. If you are pulled over for what ever reason, they give you a warning. After that its a $80 ticket. My friend was driving with his permit and got pulled over for driving with out his headlights and they gave him a warning for the license and a ticket for the headlights. The second time he got caught was for speeding, they gave him a speeding ticket and a $80 ticket for not having someone 21 or older next to him with a license. After a few times they will take you license away and you would have to wait till your 18, or go to court. Depends on your state. Seems most states are the same.
here in damn wisconsin if you have to drive with permit you need someone who have his driver lincence for 2 year. If you get caught you won't take they test driving and they will take the permit away from you until you 18 years old.
thank you livewire, basically the exact answer i was looking for, here in tx you have to have someone 21 or over with a year of driving experience next to you if you have a permit