To hear some classical music administrators tell it, you’d think that getting young people to a performance was a task worthy of Hercules and Sisyphus combined. But Washington National Opera doesn’t seem to be having any trouble. “The company’s sold-out performance of Gaetano Donizetti’s L’Elisir d’Amore showed that it is about more than low-price tickets, though that certainly helps. It is about creating a social atmosphere and making sure the quality of the artistry is there.”