Over the past 4-5 years, the trees leaves are progressively getting thinner, and the tree is losing its canopy. I would say that there are a growing number of very small branches that are dying. I try to remove these as they develop, but the tree is about 20 plus feet high, so I can't always reach them. The tree is about 30 years old. Is it just too old? Would it help to trim some of the established but thinner branches? The leaves look healthy and I find no signs of disease on the trunk.
Japanese Red Maple Tree
Certified GKH Gardening Expert
It could be too old, but these trees tend to be longer lived than this. 30 would be on the low end of its life expectancy.
It could possibly be a fungus or, less likely, a pest. Treating the tree with both a fungicide and a pesticide will treat both possible issues.
Ideally, I would recommend having a tree specialist look at the tree. Many tree problems are very hard to diagnose without being able to visually inspect the tree.