peach tree

Question

Makes a lot of fruit but only gets about walnut size and does not mature.

Answer 1

This could be due to pests, disease, pollination issues or too much fruit on the tree.
Here are some links with more information.

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