Dating is done usually by dating organic material found with a site. If you find flint tools next to a butchered animal carcass, for example, you can do isochron dating on the carcass to date it, and thusly the tools by association. Since most tools from a given era look similar, you can date other tools from the originals, given that all of the tools are found in the same geographic area.
Making a drastic simplification: let's say I used that axe ten years ago to butcher an animal and someone found the axe today, along with the carcass. Date-by-association would make the axe ten years old, more or less.
Not trying to be argumentive here -- just wondering how they can be so sure they aren't dating the actual rock material itself, rather than the axe-creation date?