There is a breakdown of growth/weight by age in the book "Giant Snakes" by Clifford Pope. I beleive he only gives exact info for the first 3 years and then general size info for the following 10 years or so. Sorry I can't give the info here, I already returned that book to the library. It's an older book (from the 60s) but lots of interesting info about size/temps/history of retics, burms, etc.
Amazon.com: The Giant Snakes: Clifford H. Pope,... 
