Should an 18 year old report gambling winnings on his taxes?

[Psyonic]

In the US, If an 18 year old is playing poker online at sites that only require you to be 18 or older, he is acting just as legally (maybe it's not legal, but just as legal for an 18 year old person as a 40 year old person) as any other American playing online poker. But considering there are no B&M places in America for under 21 gambling (that I know of) should he report it on his taxes?