Legitimate offshore casino sites are not subject to state and federal gambling restrictions, creating a backdoor that 18+ players across the USA can benefit from to gamble online.
There are no states in the USA that regulate locally licensed online casinos or apps that are available to those of you who are between the ages of 18 and 20. The states of Connecticut (CT), Delaware (DE), Michigan (MI), New Jersey (NJ), Pennsylvania (PA), and West Virginia (WV) license online casinos that allow 21 and over gamblers to play real money casino games online. This is one reason that 18+ offshore online casinos have gained such strong momentum.
While some forms of state-regulated online gambling are spreading like wildfire across the US, sports betting specifically, online casino games are not as common at the state level.