Of course, they are fossils now. I found a link here which states that herbivors lived far longer than carnivores. The example being a T-Rex being "old" at 29, and a herbivorous Bothriospondylus having not reached half it's adult size at 43 years old.
But, is there any evidence that can indicate their life spans, or life spans of at least one kind of the dinosaurs?
An additional brief question is are their lifespans comparable with modern day descendants?