Customs on return from cancun?

I am going to cancun and returning on may 26th. It is not a direct flight and I am stopping in North Carolina with an hour and fifteen minute layover, before the flight to Boston. Will I have to go through customs upon arriving in North Carolina or in Boston. Also, my uncle requested a bottle of Don Julio Tequila, but I am not 21 years old, but I am old enough to purchase liquor in Mexico. Will I have trouble getting this through the airport. I know your aloud 2 liters of alcohol and will put it on my customs form, but was wondering if age is an issue.