“On Wednesday afternoon, Aran Bell, at just 19, makes an important debut: as Romeo in Kenneth MacMillan’s production of Romeo and Juliet. At Ballet Theater, such a leap for a relatively unknown dancer is rare. Dancers wait — and sometimes really wait — for a featured variation in a full-length ballet. But a lead like Romeo? It’s as if Ballet Theater plucked a page from the casting manual of New York City Ballet, which often throws young dancers into principal parts.”