For several years now I have had ridges on my thumbnails. Both hands. They are perpendicular to the side cuticles and in some cases are very deep? As a rule I have always had a ‘stress induced tic’ of picking my cuticles. This happens to millions of people across the globe, so it is nothing new. But I was told the ridges are not caused by a fungus…Does anyone know what causes the ridges? Could it be the picking? Is there a cure?
As I grow older I get these on all my fingernails. Maybe you just aren’t there yet. 
Things get out of whack with the amount of nail being produced. I have them on all my fingernails and toenails. I also have a fairly severe angle on my left thumbnail, probably the result of some damage to the nail bed.
I actually think they look kind of cool.
This link has some great answers to your question!