We have 7 mature trees but they do not produce nuts. We live in northern Indiana.
Typically, when this happens, it is due to improper soil nutrition ratios. When there is too much nitrogen and not enough phosphorus and potassium in the soil, then the tree will not produce.
The tree will prefer less rich soils, so be sure that the nutrient levels are not too rich for the tree. These articles will help:
https://www.gardeningknowhow.com/edible/nut-trees/buarnut/buartnut-tree-information.htm
https://www.gardeningknowhow.com/edible/nut-trees/walnut/butternut-harvesting.htm
https://www.gardeningknowhow.com/edible/nut-trees/walnut/growing-butternut-trees.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/test-soil-for-pests-and-diseases.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/making-sure-soil-drains-well.htm
They look full growed?
This is much too early for fruit to be ripe. I would suggest keeping a close eye on how much water the tree receives. Though they like deep watering, they will not tolerate wet conditions. This includes compacted or clay soils.
Unfortunately, in order to remedy the situation you will need to find the condition that is responsible. Then, all it takes is removing the stress and providing the correct environment.
https://www.gardeningknowhow.com/edible/nut-trees/buarnut/buartnut-tree-information.htm