Can a fourteen year old take ibuprofen tablet?

Safe dosing for ibuprofen is by body weight. The dose is:

10 mg per kg., but not to exceed 800 mg in a single dose

1 kg = 2.2 pounds. If a person weighs 110 pounds (50 kg) they could safely take 500 mg of Ibuprofen. If a person weighs 130 pounds (59 kg) they could safely take 590 mg of Ibuprofen.