Young artists on the cusp of their careers come out of Boston-area art schools every spring, an event marked by thesis exhibitions around the city. Now is the time for viewers to discover emerging talents. In the past, the School of the Museum of Fine Arts, Massachusetts College of Art and Design, and Boston University have ushered out such art stars as Doug and Mike Starn, N.C. Wyeth, and Brice Marden. Maybe one of this year's grads will hit it big. We spoke to six promising young talents with shows up in April and May.