Betta indents around mouth.

So I've had my betta for about 2 years.
A couple of months ago I noticed that indentations formed around her mouth and gradually became holes on each side between the upper lip and head.

For the life of me I couldn't figure it out and she was active/eating as always so I let it be.

These past two weeks she's been lethargic and laying under shelter, but actively eats a lot.

Has anyone heard of these indentations around the mouth that later become holes? I was thinking it could be a bacterial infection or hexamita but there's no fin rot or anything else.
Could it possibly be just old age?