When we pick up folks in FRA, we plan to be there about 20 - 30 minutes after the projected arrival time. Flights from the states can arrive early, so it is a good idea for your son to check before he leaves to the airport. Parking costs 4 EUR per hour.

We usually pick up folks just as they exit the baggage claim area, but the meeting point might be an even better suggestion, at least as a back up.