I do wonder about Utah. The partisan age divide is exceptionally intense there.
but also overstated
Trump still won the youngest voters, albeit by a point.
However, isn't gender divide largest amongst millennials? Generally married couples more often than not tend to vote same way so divide tends to be biggest with unmarried types and you have far more unmarried amongst millennials than you do other age groups. Only one maybe similar is seniors with how number of widows but usually by then voting patterns are pretty set.
I would say amongst millennials, Trump's support outside South where divide small was likely him getting around 5-7% more amongst male millennials and 5-7% less amongst female millennials.