We have had enormous amounts of rain this spring and one hard freeze, but our peaches are lovely for about 2 days, then they develop this moldy spot and they become totally molded!
What Is Causing Brown Moldy Spots on Beautiful, Bugfree Fruits
There are many diseases that attack peaches. This article outlines some common ones: https://www.gardeningknowhow.com/edible/fruits/peach/common-peach-diseases.htm. To find out exactly what is afflicting your tree, and how to treat it, take some samples of fruit, leaves and twigs to the nearest Extension Service. This link will help you locate one: https://www.gardeningknowhow.com/extension-search/