Every Dinosaur has it's own growth multiplier, or how fast it grows. The lower the number is the faster it grows.
As a general Rule herbivores tend to grow faster than carnivores(with the exception of large sauropods like barosaurus and sauroposeidon).
The growth multiplier of a dinosaur can be viewed in the dinosaur selection.
The growth multiplier is also (about, it's off by a few minutes) how long in hours, it takes to get from start to elder. For example, triceratops has a multiplier of 0.8, so it takes 48 minutes to get to elder.
View growth rate multiplier for more information.