The preferred method of dating dinosaur fossils is with the radiometric dating method.
And the result of this accepted method dates dinosaur fossils to around 68 million years old. Its half-life ($t_$) is only 5,730 years—that is, every 5,730 years, half of it decays away.
Many people are under the false impression that carbon dating proves that dinosaurs and other extinct animals lived millions of years ago.
It's accuracy has been verified by using C-14 to date artifacts whose age is known historically.
The fluctuation of the amount of C-14 in the atmosphere over time adds a small uncertainty, but contamination by "modern carbon" such as decayed organic matter from soils poses a greater possibility for error. Thomas Seiler, a physicist from Germany, gave the presentation in Singapore.
The age they came back with was only a few thousand years old. And kept their theory that dinosaurs lived "millions of years ago" instead. They then use potassium argon, or other methods, and date the fossils again.
This date did not fit the preconceived notion that dinosaurs lived millions of years ago. They do this many times, using a different dating method each time.
The results can be as much as 150 million years different from each other! They then pick the date they like best, based upon their preconceived notion of how old their theory says the fossil should be .