Of course it is just possible that you might decide in due course that aviation (of any sort) isn't the career for you. Many people have a strong idea of career choice in their mid-teens, but change totally by mid-twenties. Getting a degree (not necessarily aviation-related) keeps your options open, and university is still the best chance most people get of studying a subject just for the pure hell of it (even if it does seem like hell some of the time
).
As some have said, there are degree subjects relevant to aviation, but a degree in anything is no disadvantage to a career in flying. A colleague of mine was a graduate accountant (and a very good one, I gather, not that I know much about accountancy) and she decided to take up flying and is now flying heavy metal.