We know that X-men first class, X-Men: Days of Future Past take place in the 80 or 90 and X-men, X2, X-Men: The Last Stand take place in the 2000. I will predict the new mutants movie will take place in the 80 or 90. Since class, X-Men: Days of Future Past, x-men apocalypse telling the origins of Professor X, Magneto, mystique. I think new mutants will focus on a young Scott,Jean and Storm. I don't think Fox cast these young actor/actress just for x-men apocalypse. These are the future of the franchise.