Let's just say that it's 8,000 years.
Well, we don't have anybody who has gone back to even 5,000 years to count tree rings, and to observe them being laid down one per year. We don't know that trees back at 5,000 years didn't lay down 10 rings a year for a 500 year period, or maybe, only 1 ring every 10 years for a 500 year period. And we don't know if the cosmic energy that makes C-14 wasn't the cause for lesser or greater C-14 AND lesser or greater numbers of tree rings per year for certain time periods.
Because of this, the carbon dating science is all assumptions. If scientists and books said, "We assume, based on da da da," It would be okay. But the emphasis is that this science is fact when it's only assumption. Such makes it to not be science at all, but rather, fable... with emphasis on the Bull.
In fact, that's how scientists treat a whole lot of things. They form a hypothesis, and find a way that the hypothesis could be real. But they ignore or pooh, pooh all kinds of things that show that reality could easily be a whole lot different. To see that this is true, take a look at some of the other things that Graham Hancock shows us at https://grahamhancock.com/.
Carbon 14 half-life is 5730 years. Carbon-14 dating is reliable to about 3 half-lives or about 18,000 years. Isotopes of other elements can also be used to estimate fossil ages beyond 20,000 years. Potassium 40 half-life is 1.28 billion years.
BTW, tree rings mark the end of summer. See summerwood/latewood.
For a tree on this planet to grow 10 rings a year, you would have to have an environment with 10 summers/fall/winter/springs a year, and a 10 fold increase in Sun activity, LOL. You are basically talking nonsense.
Basically and simply I am saying that nobody knows what happened in the distant past.
We don't know if C-14 wasn't dumped onto the earth in large quantity from a meteorite or not. We don't know if God created all the C-14 on the 4th day 7,500 years ago, just to make things work, or not.
We don't know if in the distant past, tree rings were formed every week... or if the times they were formed varied or not.