Like all reptiles, they continue to grow throughout their lives and many other factors influence their grow. Such factors as temperature, food intake and general overall health of the animal. You should expect the first three years to demonstrate the most amount of growth. Sexual maturity is reached in around 18months for males and 22-24 months in females from my experiences. I have several female borneos (P. breitensteini) in my collection that are 4-6years of age and weigh between 16-24lbs. These supposedly get smaller that the red bloods (P. brongersmai). I have a male borneo that is roughly 7 years old and almost 6 feet and weighs a lean 24lbs 
Other people have much older P. brongersmai that are at or almost 7ft and 30 lbs. See what you get to look forward to!
