Yes, you can give your 9-year-old son an adult dose of 500mg of acetaminophen if he weighs 180 pounds. It is recommended to give him 1 or 2 tablets of Tylenol extra strength. You can repeat this dose every 6 hours if needed for pain or fever. If he has difficulty swallowing tablets, you can give it to him in liquid form or crush/cut the tablets and mix them with food or liquids. Make sure to consult a doctor if his fever does not go away within 48 to 72 hours or if his condition worsens rapidly. Wishing your son a quick recovery.