I developed myopia between the ages of 17 and 19. I know this as I took my driving test at 17 without glasses, failed it.. then needed to borrow some for my 2nd attempt 2 years later.
You might notice I don't wear them nowadays... laser treatment was the best 2K I ever spent.
Doesn't sound like that was liked to too much time in doors, guess it's one cause among many.
2K sounds like a bargain!