he coulda had a c-14 disease in his body that could have depleted the c-14
This statement leads me to believe that you either don't understand "c-14", "disease" or "deplete".
I'll try to clear this up.
c-14 is a naturally occuring version of the carbon atom in our atmosphere. Therefore, anything interacting with the atmosphere (breathing) or interacting with things which interact with the atmosphere (eatting them) will be exposed to C-14 on a regular and ongoing process.
The carbon which exists in your body got there somehow. It did't just appear. So, within your body right now, a certain percentage of your carbon is c-14 carbon. And, as long as you keep breathing and eating, that percentage is going to stay the same as it appears in the atmosphere.
This is true for all living things.
When you say "disease" I assume you mean one of 3 things - either bacterial infection, viral infection or non-infectious degradation (heart disease, cystic fibrosis).
In all these cases, the "disease" is comprised of living matter, which like "all living things" as stated above, has the same percentage of c-14.
Now, there are conditions which exist which reduce the body's iron for example. But there are no conditions which reduce the bodies carbon. Carbon is the building block, hence the term "carbon-based life".
Even if there was a condition which reduced the amount of carbon in the body, it could not selectively remove the carbon-14 from the molecules to which it is attached. It could only blanket remove carbon.
Since the proportion of C-14 to regular carbon is stable, removing any amount of carbon will have no effect on the proportion of c-14 in the body.
When the living thing stops interacting with the atmosphere (dies), it stops replenishing the C-14 in the body. At this point, the percentage of C-14 starts to decrease.
Eventually, all the c-14 has decreased, causing an end date to this measuring method.