I've have keratoconus symptoms since I was teenager, but wasn't diagnosed until my mid-20s. It's been over a dozen years since then, and my condition has not degraded. Of course, I've never flown anything.
Keratoconus as a disease has enjoyed a renaissance of late. Corneal topography has allowed even minor forms to be diagnosed with incredible accuracy, whereas in the past, only severe cases would be noted. I'm serious: I went through several years of being told it was "normal" to see ghost images of everything. At the same time, they now make keratoconic RGP lenses that are considerably more comfortable than the old bog-standard ones, so they don't pop out or bring dust right to the cornea as easily as they used to. Although, to be honest, I've done just fine with glasses the last three years, and my job requires extreme visual acuity.
Effectively, the increase in diagnosis rate has revealed that, alongside the "old school" keratoconus, the chronic, degenerative cornea disease that ultimately requires transplants, there's a much more common version with an onset in the teenage years that stabilizes in the mid-twenties with minor cornea degradation. It's a nuisance, but shouldn't be an obstacle.