Since this student has a verified disability due to the Down Syndrome he probably has an Individualized Education Plan as per the federal law IDEA. I would call an IEP team meeting as soon as possible and put that he may play football with his teammates since we have to look at social/emotional well being of our students on his IEP. This age requirement might be waved in the modifications/ accommodations in the Iep. IDEA is Federal law and may trump rules by the state.