Lots of threads on this board about what will and won't get you punted from the recruiting centre.
I will tell you this though: I wouldn't lie about anything you ever get asked about. As an institution we are much more forgiving about people being open and admitting their errors as opposed to catching someone in a lie.
As a side note, I would be very surprised if anyone in uniform ever didn't have a few drinks before legal age. However, every time you choose to do something, think a bound ahead and weigh the consequences.
I'm not telling you to do or not do anything, but manage your risks. If you have a couple in your basement with your friends, what is the worst that could happen? Now compare that to having a few and driving around with your friends? I'm pretty sure getting an underage DUI and manslaughter charges would probably curtail your career advancement.
You're an adult now or will be very soon. Time to start weighing pros and cons and making decisions that will have consequences.