Who told you that ?
Physics, Cosmology, Geology, Chemistry. They all independently attest to the age of the earth and universe.
and what do they reckon started it?
There are many ideas and hypotheses, however currently the correct answer is "no one knows". But more importantly we need to try and understand if that is even a valid question. Time and space "starting", may be a flawed concept to begin with.
Suffice to say, it is complex. But we know what we shouldn't do, and that is claim to have the answer when we don't have any evidence, as religion does.