Units can't Level Up

I want to add units can't level up start at the 0 and end to the 10(20)(30) or (50) to made a worker (minion) level up you only need to make the minion do their specialities like Swordmen = Fighting , Bowmen = Hunting and Fighting etc. per level the minion receive = 0.25 Attack , 1% Deffence , 0.5 Healt , 0.4 Speed , 0.2 Range (For Archers) , 0.2 Extra Gold (For Bandits)