Is 500 mg amoxicillin to much for 65lb boy?
No, this dosage is right if it's given twice a day. 500 mg twice a day is fine for most infections. He must be not allergic to penicillin.
ADDED: This is not the place to seek specific medication advice, especially for a third-party, and a child at that. The proper person to ask is your doctor who can diagnose the actual illness and prescribe the proper medication and its dose, for the individual patient.