|"Jane" a Juvenile Tyrannosaurus (image Wikipedia)|
The growth pattern of Dinosaurs can be roughly summarized as a number of years of slow growth, followed by rapid growth until maturity and gradual growth until death. Depending on the size of the Dinosaur it could take anywhere from 2 years for the smallest species, to 15 years for the gigantic Sauropods to reach maturity (quite amazing if you consider the size of the largest Sauropods).
Tyrannosaurus had a surprising twist on this pattern. Much like humans T. rex did not start its fast growth until around twelve years old, and would then grow rapidly until reaching maturity at 18 or 19 years old. Compare that to the basal Tyrannosaurid Guanlong which was found to have been mature at a mere seven years of age.
It has been suggested that the reason that Tyrannosaurus enjoyed such a long infancy and adolescence was that the juveniles filled the ecological niche normally occupied by medium-sized predators. So far no medium-sized carnivores have been found that shared an environment with T. rex. The "King the Tyrant Lizards" was definitely the top-predator in it's environment, it was probably also the dominant medium-sized predator.
|"Sue" a mature Tyrannosaurus (image Wikipedia)|
Like most Dinosaurs Tyrannosaurus rex grew fast, and died young.