EXCLUSIVE: Amazon MGM Studios is opening their $15M Sundance pick-up, My Old Ass, on Aug. 2 in a limited rollout. The LuckyChap and Indian Paintbrush production comes from director/scribe Megan Park and stars Maisy Stella, Aubrey Plaza, Maddie Ziegler, Percy Hynes White and Kerrice Brooks. Pic follows bright-yet-irreverent Elliott (Stella) the summer before college as