how long will bad credit follow me?

I used to be really bad with money, and was terrible about paying my bills. I recently got a much better job and have been paying everything off. I only have 1500 left to pay off until I am on top of all my finances. How long will it take me to build back my credit after everythign is paid off? I have had issues renting apartments and stuff in the past. Just wondering, and some advice, NEVEr let yourself get behind on bills! I WAS SO STUPID, and if I had known it would mess me up this much, I really would have never done it. Educate your kids on credit! THANKS!