Knowing the age of fossils can be somewhat complicated unless you have done enough research to know the details. There are some people who learn how old the fossil fuel is not based on the amount of carbon that can be found but by comparing it to the other fossil fuels that are available.
There are also some that may come up with the age of the fossil fuel-based on the layers of rock that the fossil fuel has. Based on the details, the age of the fossil should be known based on carbon dating, which is not usually done.
The carbon of -14 is only applicable to fossil fuels that are younger than 75,000 years. This type of fossil fuel has the tendency to decay a little bit too fast.