Quote Originally Posted by Simetrical
Middle-Aged trait gives a bonus to movement instead of a penalty.
Young agents (diplomats, spies, and assassins) get a boost to movement of 10-20%; once they become middle aged, this bonus is lessened to 5%. Hence, they're not as fast as they used to be, but still are able to move further than they could in vanilla. Not a bug, it's a feature!

If it's happening with generals, that's another matter. Middle-aged generals should get a 5% penalty to movement.