Well, just heard tonight: The fruit is very edible! This afternoon, Dad went out to the tree to check on it, and one of the peaches on the lower branches came off in his hand, so he figured it must be ripe... took it indoors to compare with a store bought peach, and tasted them both.

The volunteer was much sweeter, and juicier and all round yummier... Yay!

Okay, now here's a second question from me:

This is the first I learned how big the tree is (well over Dad's head), and that it is several years old. So why is this the first year that he noticed any fruit growing? It's at the edge of the yard, but it's not hidden, by any means -- and Dad's very observant, generally. Do some species of peach take several years to mature?