You have to be eighteen and they will require the DOB and SSN of the additional card holder.

You have to be 18 (in most states, if not all) to enter into a legally binding agreement such as signing a credit card receipt. Most credit card companies (virtually all of them) have no problem with ignoring that issue on the basis that they can stick it to the primary card holder. However, AmEx is significantly more strict when it comes to this issue.

From a business perspective, I agree with AmEx on this one. The risk is pretty high and the amount of potential lost business from the <18 crowd is (generally speaking) minimal by comparison.

Regardless, if you mislead AmEx about his age, it will not be a problem as long as your account is kept without incident. There might be a bit of confusion when your son applies for his own card once he's >18, but it's trivial to clear up.

Hope this helps. Cheers.