If there is too much daughter product(in this case nitrogen-14), age is hard to determine since the half-life does not make up a significant percentage of the material's age.
This means that lifeless organic matter is effectively a closed system, since no carbon-14 enters the organism after death, an occurrence that would affect accurate measurements.
According to the YEC argument, if one can determine how fast an element is entering the ocean, such as from rivers, and how fast it is being removed, such as through chemical reactions on the sea floor, one should be able to determine a maximum age for the oceans. Jeanson stated that the oceans could not possibly be older than 62 million years old, a number commonly given in YEC literature.
I have addressed this issue a couple times in the past (see The YEC “salty seawater” argument—not worth a grain of salt and Aluminum and the 100-year old oceans).
Some background on Rubidium and Strontium: Rb is a highly incompatible element.
Sr is fairly incompatible in mafic systems and relatively incompatible in silica-rich systems.