They pretty much go through growth spurt until 18 months old and after the growth rate slow down, but reptiles grow throughout their lives...just a tiny bit a time. I know a 10 year old Cyclura, a type of rock iguana from the Caribean, that was still growing. Last year he weigh less and was shorter SVL, but this year at 10 years he surprised his owner by growing another inch or so and added some pounds.