For II, it's okay. II T&C provide that "Individuals under the age of 21 are not eligible to receive a Guest Certificate."
However, you might want to check with the resort you want to send him to to be sure. The very next sentence in II's T&C states, "Additionally, the issuance of a Guest Certificate and the use of the Host Accommodations are subject to any restrictions or limitations that may be imposed by the Host Resort."
Likely you won't be responsible. The resort will ask him for a credit card imprint upon check-in which will be used for any charges or damage.