Mature and Able to Reproduce Around Age 10 - Tenontosaurus & Allosaurus

Research from the University of California, Berkeley, and other institutions has revealed that "dinosaurs matured and were able to reproduce relatively early."

They searched for a tissue called "medullary bone," which is seen in female birds during their egg-laying period, in dinosaur fossils. This tissue helps in forming the eggshell.

As a result, they discovered medullary bone in the fossil of the ornithopod Tenontosaurus from 125 million to 105 million years ago, and from the growth lines (like tree rings) in another part of the bone, it was estimated to be 8 years old. This means that Tenontosaurus, a relative of Iguanodon, could lay eggs at the age of 8.
In addition, medullary bone was also found in the fossil of the large theropod (carnivorous dinosaur) Allosaurus, estimated to be 10 years old, indicating that it was capable of reproduction at that time. The lifespan of large carnivorous dinosaurs is estimated to be about 30 years, so it seems they could lay eggs from a relatively young age.