My 18 yo son was recently diagnosed with epilepsy but he wants to play college football. Should he?

Poor choice of sport. It is generally not recommended that people with epilepsy play contact sports like football.
Possibly. It would depend upon a number of factors: are his seizures well controlled? Is he having side effects from his anti-seizure medication? What is the cause of his seizures (if known)? There are numerous high school, college and professional football players with epilepsy. In general, most are doing well. Nonetheless, there is a risk of worsening of seizures with repeated concussions.
Epilepsy. If it is controlled very well, he may play football. He needs to avoid concussion.He nneds to takes his medicine. Neurologist clearance is must.
Depends on history. If epilepsy is from a prior head injury, probably not a great idea (risk of repetitive head injury and reaultant complications), but in general well controlled epilepsy itself would not preclude participation in football.
Depends on situation. Many forms of epilepsy are well controlled with medication & a full & challenging life including sports is possible.What applies in your case is more specific to your sons form of epilepsy & response to treatment.