Post-apocalyptic meets The 12 Steps. T. These clean and sober men and women are not a dull lot. Sex, drugs, and bluegrass music in a 2077 western United States, rebuilding after the world almost came to an end. This is an adult book for 16 and above. It is not a kid's book. Appropriate for all adults, and not just for members of 12 Step Fellowships either. Something for everybody. Fast paced, funny, serious and sweet, Air & Gravity will not disappoint.