Underage Gambling
I have no idea of how tall or big-boned you are or are not, or, whether you have fine or rougher-looking features. It is much easier for a 19 year-old girl to dress or make herself up too look older, perhaps at the risk of looking like a hooker, than for a 19 year-old guy to do the same. When I was 19, I looked about 16, and, I am of average size. I would never even try it. I was over 21--the minimum age in Atlantic City was 18 then--when the first casino opened in 1978.
Find out whether it is illegal for an underage person to play in the state in which you intend to play. It is illegal for a casino to allow an underage person to play, but it may not be illegal for an underage person to play. Avoid doing anything unlawful! Suppose that it is not unlawful for a minor to play, but you get caught. You will not be allowed to keep your winnings because your wagering contracts were void and not enforceable. You may be backroomed. Casino guards in Atlantic City are now permitted to detain persons suspected of underage gambling or drinking.
Usually players are interested in disguises to hide their advantage play, especially if they have been backed-off or trespassed. Playing after being trespassed can get someone into legal trouble.
Two principles of disguise are: Wear a disguise that draws less rather than more attention to you and wear a disguise that you can really pass as. I will assume that you really are from Brooklyn for this illustrative example. Someone once asked me whether dressing in Hasidic clothes would be a good disguise for a counter who has been backed-off or barred. My advice was that this disguise would likely draw attention to him, especially in a location like Iowa. It would draw less attention in Atlantic City, but it still would draw attention. Then, it is too easy to blow your cover by doing things like being in a casino on Friday night or Saturday, or, eating in a casino restaurant.
My idea of a good disguise is to look like a typical tourist. Wear a new tee-shirt from one of the casinos and a pair of jeans. Dress in a manner that fits your level of play. Do not wear anything torn or worn out if you are playing high stakes.