Certified GKH Gardening Expert
Crabapples can live past 40 years, but then may show decline.
The spots could be apple scab, a fungal disease. It does cause spotting of leaves followed by dropping. The good news is it doesn't usually harm the tree. The best recourse is to rake up the infected leaves and destroy them so as not to spread the disease.
You may want to take some leaves to your local Cooperative Extension Service for a positive identification.