Truth be told, we don't know the max lifespan of Tyrannosaurus. Field Museum scientists think that Sue may have died from a parasitic disease in her jaw that caused her to starve to death. In captivity, crocs have held that have been believed to have been over 100. There's also birds that have been known to live a lifespan comparable to a human. For all we know, Rexy could be middle-aged, or even younger. T. rex were tough animals. Sue had multiple broken ribs, and arthritis in the legs, arm, and tail, and likely died from a parasite not from old age as previously assumed. Rexy is also once again the largest predator in North America. Nothing would mess with her except Blue, and Blue and Rexy seemed to put some distance between themselves after escaping Lockwood Manor.
Also keep in mind that reptiles that have lived in captivity typically live longer, healthier lives than reptiles in the wild. They're regularly checked for disease, are regularly cleaned, and regularly fed. As Zia said, take a caveman that could have lived 30 years max, give him dental, health care, and clean food/water, he could live three times that long. Rexy has lived this lifestyle. She was wild for only a few years between JP and the construction of JW. And only for a few years between JW and FK. She's lived most of her life being pampered in captivity.
I think we could see Rexy live to be 70+ in the right conditions.
_______________SOMETHING HAS SURVIVED