system
Given the following post, respond as if you're commenting on Reddit:
human
Do we know how long dinosaurs lived?

I'm talking about each individual dinosaur, not the time period. Did T-Rex live for 10, 50, or 100 years? Do we have this information?
gpt
Yes, we do. For some.

Or at least we have an idea.

Animals tend to grow seasonally, with more growth in warmer weather and less in colder weather. This results in what are called "lines of arrested growth" or "LAGs" for short. As an analogy, you can think of them sort of like tree rings for animals.

Now, for some dinosaurs, we can make a cross-section of their bones and count their LAGs (note, this does not always work for a variety of reasons including bone reworking through life and such). From this we can estimate age-at-death.

For example, "Sue," a large and very complete specimen of *Tyrannosaurus rex* currently on display at the Chicago Field Museum is estimated to have been ~35 years old when it (despite the name, the sex is not known) croaked. And "Sue" was an *old* tyrannosaur, practically geriatric. 

From bone histology and LAGs we can also make inferences of how fast dinosaurs (and other animals) grew. For many even very large dinosaurs, the answer is surprisingly fast, reaching adult size in often <10 years.