Will a poor employment history ruin my chances of becoming a firefighter?

I have a pretty poor employment history. I was a stupid kid and walked out of pretty much every job I've had (no call/no show). I'm 23 now and have since matured quite a bit. I have been with my current employer for over three years now. I am very interested in becoming a fireman and I know there is alot of competition for the position these days. Im just wondering if my poor employment history is going to completely ruin my chances at getting hired.