That's not a question that can be accurately answered in reality, as you will obtain different growth rates, even among litter mates, and different locality.
But as an "Average", I have found it like this for Colombians...
Born 12-24 inches
2-3 1/2 ft year one
3-4 1/2 ft year 2
5-7 ft year 3, at which point the length starts slowing down in growth, but body starts to fill out some and put on more girth.
I would say the numbers in the middle of the range I've provided are probably closer to an average. Low numbers being slow growers, and large numbers being the fast growers. But they will grow through out their lives, slowing down as they mature. I have an 8 1/2 yr Colombian that is 8 ft. +/-
Some Central American locales are born smaller, grow at a slower rate, and may only top out at 6 ft. or smaller. I have a 2 yr old Honduran that is smaller than my 1 yr old Colombians.
Some blood lines are known for reaching monster proportions as well. My mom owned a 13 ft Colombian female when I was younger.
So as you can see, there is more to it than just being a BCI.
Hope that proves helpful.
Rick