C14 was never used for dating the Earth. C14 is used for dating organic remnants. Earth "creation" first was dated using uranium-lead method. "Creation" is in quotes because it is actually date of creation of minerals, not date of completing Earth as planet from them,

Half-life means that after that time half of unstable isotope atoms will decay, that also means that other half will still be here, so if there is a quarter of atoms, than two half-life periods passed and so on. Half-life is not maximum age you could detect using that isotope.

Radioisotope method does not show the age of some object, it shows the date of creation of substance this object was made from. So dating any man-made objects using this method is senseless. Dating the age of some wooden chest gives the date when trees used to make planks grew, not the date when that chest was made, f.e..

С14 method works for organic because percentage of C14 in atmosphere is constant - it decays, but at the same time continously created by space radiation in highest layers of Earth atmosphere. But when C14 is tied by some plant into some organic composition like wood, there will be no creation of new C14 and it will slowly decay, halving its content (and so number of decays per minute per gram of carbon) each 5700 years. Content of C14 in atmosphere is very small (10e-10% of all C that gives 13 decays per minute per 1 gram of athmospheric C), so the maximum age that could be confidently dated by C14 is only 50000 years. So, when you see something like "it have an age of half million years dated by C14 method111!!!!" - it is a complete bullshit.

To date older things, other, more stable isotopes used. But most minerals will obviously just show the age of Earth components creation.