I'd use it. That old and weathered, assuming it hasn't been sprayed with something toxic recently, it should be well-leached out.

Dave

I would use it but it doesn't cost much to be safer and beautify your space at the same time by dedicating the first 6" or so to non edible companion plants. Preferably something that will keep you from disturbing that soil. Might even think about flashing it.

Different studies will show different results but they don't force things off the market for no reason. Still, the stuff is already on the planet and on your site. Since we know better_now_a little creativity with care might go a long way to reduce exposure to risk.