Right here. Did you not read your own evidentiary citation?
Most people think the idea of billions of years comes from radiometric dating. But clearly that’s not true, since this dating method was not developed until the beginning of the 20th century, about 100 years after Hutton died. Hutton based his idea of an old earth on an assumption. It was not a discovery. He assumed that the same slow processes eroding the Scottish highlands in the present formed the ancient rocks by the North Sea in the past. So an old earth is the outworking of an unbiblical philosophy (cf. 2 Peter 3:3–7).