By Vicky Hallett</strong, Special to The Washington Post What do John Boehner, Bonnie Raitt and prisoners at Sing Sing have in common? Like 36 million other Americans, they do yoga, according to the April/May issue of AARP The Magazine, which features a special health section on “The United States of Yoga.” It’s an ancient practice, after all. It’s also one that doesn’t discriminate by age.