If he is an unrelated adult he is not a dependent nor could be claimed as one.
Sorry, the penalty DOES apply to a roommate if the other criteria are met.
“The person must either have lived with you for the entire year as a member of the household (a person who is not actually related to you may meet the requirements in this way), or be related to you... “
IRS Bulletin 501 is the one about dependents.
Still haven’t seen any mention of this in the news.