In my personal canon, Methos is older than metal-working (including copper) and the first tools he made were from rock or bone. Also, Methos is 15 centuries older than civilization as we know it, meaning, before Law was invented, or at least before it spread to his part of the world. And before Law, everyone followed the alpha male, and groups of people had to be small because the alpha had to be able to dominate everyone, and if they were too large a group a new alpha would rise and the group would split into two tribes or something.

And the first time the Horsemen saw a proper city, they couldn't understand how so many people could live in such a small space without killing each other. It was probably in Egypt.

Why do I think this? Because it explains and makes unapologetic their barbarity.

Of course, this makes Methos at least, a mite older than 5000. But so what. I consider 5000 merely the lower bound of what his age could be.