Bringing alcohol from the UK to the USA?

I bought a bottle of wine for my parents that I want to pack into my checked in suitcase and bring back with me to America. However, I am over 18 yet under the 21 age requirement. I keep reading conflicting information: yes, I can bring it, yes, I can bring only one liter of it and no, I can't bring it at all. Does anyone know which one is right?