In practice yes, provided you are a little lucky and it is under a liter. I successfully did it a few times when I was under 21.
In my experience if you are a US citizen, and you do not declare anything, you are likely waved through US customs without an additional check of your bag. This is not a guarantee and depends on the customs agent's mood and view of you.
I believe there is possible random check before you receive your bags from baggage claim for smuggled goods and dangerous items. Since you are allowed to bring up to one liter of liquor undeclared a single bottle of wine or hard liquor in a suitcase is not going to raise any eyebrows. The people checking for serious smuggling are not going to waste time checking the age of each person with a single bottle in their bag.
It is my understanding if you are caught, customs will simply confiscate the alcohol. You are not violating any customs laws as long as you are under the amount that must be declared.