Our trees are old trees, here when we bought the farm 12 years ago. This year they all have lots of fruit, none of it ripened. The peaches are all the size of your thumb and hard as a rock.
Peach Trees Have Lots of Fruit, All of It Immature
Certified GKH Gardening Expert
It could be a chilling issue. If a peach tree doesn't get enough chilling in the winter, it will button the fruit, which means that it tries to grow them, but they will be deformed, stunted or fail to mature. Since no one really had a cold winter this year, it is likely that chilling could be a factor. Here is more info: https://www.gardeningknowhow.com/edible/fruits/peach/peach-chill-hours.htm
Another possibility is that there is a problem with pollination. If this is the case though, the tree will drop the fruit in late spring or early summer. The peaches cannot reach full maturity if they are not pollinated. They grow a little but then the tree aborts them. Here are some articles that may help: