When can my baby take a pain reliever without a call to the doctor first?

I have read that it is safer to wait till age of 2 years old and above. It is suggested that below 2 years old, it is better to visit a doctor first and get a prescription for pain killer. Pain reliever can mask symptoms of illness hence it is better to see a doctor whenever your children is not feeling well. http://www.babycenter.com/408_when-can-i-give-my-baby-pain-reliever-without-calling-the-do_1368477.bc