You have a good chance to beat this based on the facts. But what is also imports t is what you said to the officer. If you told the officer that you were driving, that's an admission that comes in.
You should most definitely get a full free case evaluation.
I suppose the short answer to your question is yes, you can be charged. You can be charged because the prosecution may rely on circumstantial evidence to establish the driving element of the crime of driving under the influence. In all of the cases in which no one saw the car actually move, or the alleged driver in control of the car, one has to look at ALL of the facts when evaluating whether the circumstantial evidence would support, beyond a reasonable doubt, the driving element of the crime. So even if you are charged, that does not mean that you can be, or will be, convicted. Frankly, all of the circumstances you describe about your case (i.e., the location and circumstances of your contact with law enforcement, the alleged observations of a private security company "earlier" that night, the location of the keys, the breath test, your age) seem interesting and worthy of discussion with an attorney. I hope you will seek counsel as soon as possible.
This is not intended as a legal opinion nor does the answer to this question create an attorney-client relationship, or give rise to a privilege. It is not a confidential communication.
There are two kinds of evidence. There is direct evidence (Officer say defendant driving the car) and circumstantial evidence (Officer saw defendant passed out in driver's seat, with no other people around and the keys in his possession). Sounds to me like there is a bit of each in your case. The prosecution will have the direct evidence that the car was being driven, and the circumstantial evidence that you were the driver. Also relevant will be the fact that the car is yours, which is further circumstantial evidence that you were driving. To answer your major question, yes, circumstantial evidence can be sufficient on its own for a criminal conviction. As other attorneys here have noted, that doesn't mean that YOU will be convicted, or that you should go down without a fight. I would be interested in knowing when the private secuirty says they saw your car moving. A blood test is only admissible if it is given within three hours of the driving taking place.