I would start the process and get a permit whenever he is eligible in your state and take opportunities for low-risk trips as they come. If you don't get the permit, you miss those opportunities. You don't have to decide right away what the whole process will look like. See how he does, let him get comfortable and make the time to practice. Getting a permit doesn't mean he has to drive the freeway to school right away. It can mean a Saturday afternoon trip to the park when traffic is low and you are on side streets without a time pressure.
We started with DS1 about a month after he was eligible. It took a few months to get through the online classroom portion, then getting him to the DMV for the permit, several parking lot sessions on the weekend, and then behind the wheel instruction. He just finished all that about 9 months after he was first eligible (15 here), but we are not rushed and we have found many opportunities to have him drive in the meantime. He still has another 6 months before he could get a license and we will see where he is at that point.
Mama to three boys ('03, '05, '07)