Gray Brown Spots on Loquat Tree Leaves?

I have a 3 year old loquat tree about 8ft tall in my backyard. It does not have flower/fruit yet. It was really healthy in the past 3 years. But it has gray-brown spot on its leaves, especially the younger leaves since last week; and the amount of spots has been rapidly growing on more leaves. Is my loquat tree suffering some kind of serious disease? What can I do to stop the disease and save my tree? Help please!

Hardiness Zone: 10a

By jenn from Milpitas, CA