This is the “half-life.” So, in two half-lives, or 11,460 years, only one-quarter of that in living organisms at present, then it has a theoretical age of 11,460 years.
Anything over about 50,000 years old, should theoretically have no detectable C.
So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.
That is, they take up less than would be expected and so they test older than they really are.
Furthermore, different types of plants discriminate differently.
C) dating usually want to know about the radiometric dating methods that are claimed to give millions and billions of years—carbon dating can only give thousands of years.
People wonder how millions of years could be squeezed into the biblical account of history. Christians, by definition, take the statements of Jesus Christ seriously.
This will make old things look older than they really are.
These techniques are applied to igneous rocks, and are normally seen as giving the time since solidification.
The isotope concentrations can be measured very accurately, but isotope concentrations are not dates.
Since the flood was accompanied by much volcanism (see Noah's Flood…, How did animals get from the Ark to isolated places? ), fossils formed in the early post-flood period would give radiocarbon ages older than they really are.
In summary, the carbon-14 method, when corrected for the effects of the flood, can give useful results, but needs to be applied carefully.