With Frances Ha and While We’re Young, Noah Baumbach had made a pretty convincing argument that the most recent act of his reasonably long career is the strongest. Both films tackled ideas of identity, maturity and creativity with a delicate hand and a great deal of profundity and it pleases me to say that his latest effort, his second of 2015, Mistress America sits comfortably alongside the calibre of his previous two efforts. The picture, Baumbach’s second with writer, star and all round charming presence Greta Gerwig, is at its heart a screwball dramedy about growing old, developing a personality and the…