In fairness to Chris, you're not even allowed to drink or gamble anywhere in the US until 21,
You can gamble in casinos and poker rooms at 18 in Georgia, Idaho, Missouri, Montana, Oklahoma, and Washington. In addition, you can gamble in poker rooms (but not casinos) at 18 in Florida, New Hampshire, Oregon, South Carolina, and Virginia.
In South Dakota you can gamble in Native American casinos at 18. In California it is by locality, and you can gamble in some casinos at 18. It is similar in Michigan, where you can gamble in some casinos and some poker rooms at 18.
Most states allow you to bet at racetracks, at bingo halls, and on the lottery at 18.
It is only 21 to *purchase* alcohol in the US. The majority of US states have an exception for drinking with your family (either your parent or your spouse), usually at home.
Louisiana, Nebraska, Nevada, New Jersey, Oklahoma, South Carolina merely require that it be on private property, though only parents/spouse are allowed to furnish it.
In Wisconsin, if with a parent/spouse over 21, you can drink at any location, including bars/taverns, at *any* age.
Can attest, as I have traveled to most US states and have consumed alcohol with my parents at various establishments, and gambled in casinos at 18 (though mostly for novelty as I don't enjoy gambling). I actually went to a casino immediately after my 18th birthday, and I found it boring and haven't really gambled since except to get free drinks in Vegas. (Actually got served quite a bit of free drinks in Vegas at the slots when I was 19, since they're bad at carding, both for the slots and the free drinks).