No they will fight 100% of the time after they reach 6 months which is a ballpark number.
two years ago I had bought some eggs to hatch...and even by five weeks I had to seperate the young cocks that were already starting to fight and draw blood. It can happen! This last year's never fought with each other when I finally sold one of the two roosters I had left. So this can show up early...or apparently quite late. But as stated, it's a ball park number.