What was the age of dinosaurs?

It would depend what kind of dinosaur. Small therapods like Microraptor and Compsognathus may of only had a short life span of only 3-4 years, whilst the giant sauropods such as Apatosaurus and Camarosaurus would have probably lived to maybe even 100! It all depends on the dinosaur's size. This isn't always true of course, if the animal caught a disease or was attacked it wouldn't live as long, obviously. This all just theory, but the most likely one.