Young lad, it is extremely admirable that you wish to advance your education as expediently as possible, but college is not purely about filling your cranium with knowledge; it is also about maturity. Something clearly lacking based on your short message. Why did the teacher fail you? Was it because of your lack of knowledge or capability? I'd probably say, no. It was likely for something else.
If you must know the answer to your original question, perhaps this will help you:
http://lmgtfy.com/?q=minimum+age+to+attend+northern+virginia+community+college
Good day to you!