Technology allows to establish a rather accurate value, at least in theory, thus this kind of data should be important because the planet is, firstly, the main home for every known life organism.
Curiously, if you find "earth age" in Google, it automatically appears the number of 4.54 billion years! Also surprising how some other measurements could present ages with a difference of nothing less than one billion years.
Of course, this estimation is harder than it seems for its relationship with the formation of the solar system. It needs to include some kinds of subjective elements based in what moment the planet is considered that way. Either way, it looks like it was not created spontaneously as some religions stated in the past, or even now.