
I have been giving it some thought, and how about Early Adult (EA)? That (to my ears anyway) sounds like something that would cover a much broader range of audiences. Teens would like the sound it as it sounds older to them, and those in their 20's or 30's wouldn't consider it a "kids book".
To be honest, I am surprised that anyone would come up with the name "Young Adult" for the range that it covers, not mention there already is a "Teen Fiction" category. It just doesn't fit. Early Adult certainly does a better job. You want something simple for the reader to understand, not more complex. Leave Teen Fiction for the teens and have Early Adult for the novels that fit anyone from teen to someone into their 30's and beyond.