Other mistake: Despite taking place roughly 30 years after "X-Men: First Class," Xavier and Magneto have hardly even aged. Both would have been in their late 20's at the youngest in "First Class" and in this film neither looks any older than 40. It's not because of their mutant powers either - only Wolverine and Mystique were specifically mentioned as having a slower rate of aging because of their powers.
Other mistake: During the standoff between the aliens and the mutants on the train, Jones tells the mutants to stand down, to which Beast defiantly replies with "No." When he says this, you can hear Nicholas Hoult's English accent slip through.
