It is usually possible yes as you can enter whatever details you like to during the account creation process. But that doesn’t mean that everyone is allowed. There’s always an age requirement. For US residents this can vary between different casinos and will either be 18 or 21. There’s no point in faking your details as it’s likely that you have to provide the casino with an ID before cashing out. If it turns out that you aren’t of legal age they will confiscate all of your winnings and close your account.