How do you get legendary militia in three seasons? :/
1) make a squad with 2 dwarves (TWO!)
2) make an armor stand and a barracks from it (can be placed anywhere, no requirements here, size doesn't matter, i usually put it right next to the entrance on the outside), set the barracks to train for the squad
3) give them whatever weapon you want them to gain skill in (training weapon will do) and a wooden shield
4) set them to active
5) wait one year
6) they will be legendary in fighting and their weapon skill, with shield skill lacking slightly behind, but usually shield skill is legendary after 2 years latest... Oh, and watch their attributes, if you want to have fun
This method is more efficient with guilded soldiers, as they have higher attribute caps (the skillgain gain doesn't matter, tbh)