Why do the peaches on our tree never get bigger then a golf ball?

https://www.gardeningknowhow.com/edible/fruits/fegen/reasons-for-small-hard-fruit.htm

Hi Hienergy, Here's a video that may help! https://www.youtube.com/watch?v=DhLw4t9iBXs

Good luck!

There may be some environmental causes for small, hard fruit or perhaps you need to thin the fruit earlier in the season. A properly thinned peach tree is healthier and provides a greater yield of edible fruit.

Each piece of fruit that remains on a tree must get its share of nutrients from the parent tree. When branches are overloaded, each fruit receives a smaller share. There’s simply not enough water and nutrition to go around. The result is small fruit with hard, moistureless flesh. Overloaded branches will sap the tree’s resources and weaken it, making it more susceptible to disease and decreasing its lifespan, so knowing how to thin peaches isn’t just for our eating enjoyment.

When to thin a peach tree depends on what method you choose. There are several ways for thinning a peach tree at different times during the growing season, so you should find one that best fits your gardening schedule or perhaps try more than one. All are based on the tree’s natural growth and production.

You can read more about thinning here: https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-thinning.htm

See if you don't also find this informative: http://extension.uga.edu/publications/detail.cfm?number=C1063

You are probably not pruning enough. When the tree is healthy, it will want to evenly distribute all it's energy to every leaf and fruit. A properly trimmed tree will bear fewer fruit of a larger size. For proper pruning techniques, check out High Country Gardens for a really good tutorial.

Call your local Agriculture Agent for advice as some regions are just not suitable for growing peaches.