You can’t train your characters to achieve veterancy instead, heroes and soldiers all have to fight battles to increase their ranks and abilities. Modder zedpaolo says the Sparta mod is for veteran players of Mount & Blade, and has stripped difficulty options out of the game so you have to play Sparta the way it was intended.
At least that’s the case in Sparta, a mod for Mount & Blade: Warband, that offers a trip to the fractured Greece of 431 BC and an uncompromising challenge to go along with it. If you’re going to be an ancient Greek warrior, you’re going to have to learn to fight with a spear.