Arena Stage produces some of D.C.’s finest theater. Unfortunately, it also cranks out some seriously expensive tickets, especially for its most popular shows. For youngish patrons, there’s a solution: Eight weeks before a performance, theatergoers under 30 can order tickets for the price of their age. Pay-what-you-can previews at other theaters may be cheaper, but those tickets are only available for the first few nights of a show’s run. At Arena, younger viewers can catch new shows for a decent price, and they can do it on their own schedule.