"The charging Horsemen or Highlander unit cannot be adjacent to any enemy units to begin the charge. If the defender retreats, withdraws, or is eliminated, the charging unit must occupy the defender’s hex.
Dragoons and Hussars: Dragoons and Hussars must be 1 or 2 hexes away before charging (3 hexes in Small Battles). These units for the purposes of withdrawing from a charge have a 4 morale value.
Highlander and Cavalry: Must be 1 hex away before charging (2 hexes in Small Battles)."
Does 1 hex away really mean 2 hexes away from the target (and 2 means 3, etc)? Otherwise it is not possible to satisfy the "cannot be adjacent to any enemy units" rule.
Yes, you could also phrase it that way. The idea is to measure the distance in hexes that you need to move as part of the charge in order to complete it. If you have to move only one hex to become adjacent, then you're one hex away; if you have to move two to become adjacent, then you're two hexes away.