Rexy: Not That Old?

It's often been said that Rexy is old due to her size. At 46 ft(14 meters) long and 10+ tons in weight, she would be roughly 30 years old. That's about as old as a standard Rex can get. A standard Rex. Rexy is not your standard Rex. When something is cloned, it often reaches maturity faster. Usually twice as fast. So, if a 46 ft standard Rex would be 30 years old or so, Rexy might only be 15. By the time Jurassic World rolls around, there's a high chance she'd still be alive. If Jurassic World takes place 22 years after the events of Isla Nublar, Rexy would be 37. Old, but not nearly as old as she would have been if she was 30 in Jurassic Park(52 if that were the case). Maybe good ol' Rexy was still in her prime during the first movie. Also, if she was only 15 in the first Jurassic Park and was already 46 ft long, then god help whoever encounters this giant beast in Jurassic World...