Not a stretch at all considering the very well studied nature of the over 40 remarkably complete specimens we have. We can tell how much an animal grew from the thickness of bone rings, very much like tree rings. Tyrannosaurus in particular had massive growth after their thirteenth year, matching humans maximum growth spurt sustanied over 5 years or so.

Tyrannosaurus feet bones were shaped to lock together and function as a sigle unit. This reduces the energy cost of walking and is only found in a few other groups of dinosaurs, all of which are long-distance runners. A similar situation can be seen in horses and other ungulates, and to some extent humans and wolves. Cats on the other hand have very open foot structures, being optimized for sprinting and flexibility rather than running.

As for torpor, that was an offhanded idea, thinking about it again, torpor is usually used to conserve heat, so probably not necessary for T. rex.