Maine's governor vetoed a sports betting bill in early 2020 and while the Senate and House tried to overturn it, they didn't succeed. That being the case, sports betting in Maine won't be legalized until 2021 at the earliest.
It was an unfortunate turn after state legislature approved a bill mid-2019 and sent it to the governor's office for a final signature. The bill would have regulated sports betting licenses for retail and online sportsbooks.
In addition to casinos being fairly new in the state, Daily Fantasy Sports and horse racing betting are both regulated. Fantasy sports have never been an issue in Maine and were officially regulated in 2017 with fairly generic laws that include the minimum age to play being 18 years old.