have a clause that states that no one under 18 can use the product
add an addiitonal "child" or age related clause stating that product is not to be used by people under the age of 18.
It would also be nice to be able to state that we can only sell to individuals 21 years of age or older
Or, be able to specify which age is the minimum age. For many iOS apps, the minimum age is actually 17.