The axe looks identical to those found round California, chiselled by Indians...er, Indigenous Peoples...about 250 years ago. I guess human technology didn't change much over 499,750 years.
LOL
How old would would an axehead be if someone chiseled one right now out of a nearby rock, from some ancient volcano formed a billion years ago...
Less than a week. The age of the material used has essentially nothing to do with the date of manufacture.
BTW, "chiseled" doesn't describe the process awfuly well. To be more precise, they are "flaked" or "knapped". The process consists of hitting the soon-to-be-tool piece near the edge with another stone. This knocks off "conchoidal" (shell-shaped) flakes from the opposite side.
If you look at the photos of the "axe" in this article, it has been hit so as to remove flakes from both sides (i.;e. it is "bifaced"). In fact, since I haven't seen wear patterns indicating was actually used as an axe, I (and most of my colleagues) would simply call it a "biface".
Depends on how you choose to define "how old", of course...
Different dating methods can measure different aspects, so by choosing accordingly you could find the answers to such questions as a) how long ago was it chipped into an axe, b) how long ago did it last see the light of day, c) how long ago did the rock it's made from solidify, d) how long ago did it get buried, etc.
A few hours, give or take several years.
Any arbitrary age the finder felt like assigning.
And how about this heavy revelation:
Despite being half and [sic] million years old the tool is very well-preserved