But as is well known, when you die you stop breathing out CO2, as well as ceasing to take in any more food.
So the amount of radioactive carbon in your body at death, from then on will simply disintegrate by radioactive decay.
Carbon 14 is a short lived radioactive element with a half-life is only 5,730 years approximately.
In the beginning the God created the world very good.
However, the world ceased to be very good after Adam and Eve rebelled against God and God cursed the ground in judgement.
The world degenerated even more rapidly after Noah’s Flood when the atmosphere changed drastically, and much more radiation could penetrate the atmosphere.
The simple principle is the longer you have been dead, the less radioactivity you will have in your body.
Ultimately it will be so little that it will be immeasurable. However, to use such a method you must assume the world that has always functioned the same as today.