I'm doubtful about these having much age. I saw quite large supplies of similar beads in the tourist markets in western Yunnan when I was there recently. One of the characteristics I noticed was that in any batch there always seemed to be some beads that were drilled at an angle to where you would expect the perforation to be on, say, a genuinely ancient bead. It struck me that someone was trying too hard to make them look "primitive." There are several like that on the strand that's illustrated here.

I wasn't interested in the agates, but I did buy a couple of similarly rough turquoise beads, often drilled in the same way. They're dyed turquoise, I'm sure. The seller had but a ridiculous starting price on them, claiming they were ancient Tibetan, but brought the price down by 95% in less than a minute!

Cheers,

Will