My Turkish Angora gets them pretty often. (she's been checked out by the vet to rule out med. issues.) He said it is just kitty snot and not to be alarmed.
I would have your kitty in to see the vet to rule out any kind of medical issue and then once you're in the clear just assume it's kitty snot. (they get it like we do!).
I just try to keep Izzy's clean
I take a tissue and clean her nose every day or everytime i see snot in her nose. She never sneezes/etc or has allergies issues, so for her it is just a "booger" thing
I wouldn't necessarily say your kitty will grow out of it- my Isabella is several years old now and she's never grown out of it (and she won't because she is going to produce nasal discharge for the rest of her life as will any other kitty.) -the key is just to keep the nose as clean as possible