Q.Old peach tree
I have a 20 yr old peach tree and always had abundance of fruit until a large limb fell off then last summer, then not one peach. The tree is very healthy looking and lush with leaves. What can I do to help it set fruit for this summer?
Not knowing the variety or your zone, it's entirely possible your tree is getting to the end of it's life.
Some varieties produce fruit till they are 15 to 20 years old.
Cooler climates can shorten the life of a Peach Tree, where in warmer climates with great growing conditions a Peach Tree can live 50 years.
The loss of a limb can be a stress to the plant or a symptom of other problems with the tree.
Check for signs of insect or fungus issues.
I'm listing some links to refresh you on the care requirements.