My two cats are always fighting! Help Me!?

My two cats mia - age 2 - female & lucky - age 19 - male are forever fighting! its usually mia tht starts fights as lucky likes to just lounge about and enjoy being a cat. They have started fighting ever since we got mia as a kitten! And it hasn't stopped! we cant keep them together as they fight and wen we go out we HAVE to leave them in sepertae rooms! Ive searched th net and it says wen u first get a kitten ur carts may fight at first but after a week or so they become friends and sleep with each other ( tht has neva happened!) but its been going on for 2 years now and i am fed up! Lucky is getting on in his years and I don't want his last few to be memories of being tormented by mia! help me!