Buying alcohol in the UK and bringing it into the US?

i might be going to new york sometime soon later this year and i understand that the drinking age is 21 as opposed to England's 18 . Basically i turned 18 a couple of months ago and would like to know if i buy alcohol in the airport over here will i be fine taking it through american borders? or buy it in a shop here and then place it into my check inn bag .