At 18 during my interview for Mechanical Engineering I quite confidently stated that I intended to pursue a career in consultancy engineering and eventually become a Chartered Engineer. And the basis for this? About 2 weeks shadowing at a consultancy company and thinking that it might be what the interviewer wanted to hear.
Ultimately, the reality is that when you are applying to university, or even during your degree, you may not have a concrete idea on what career path to pursue. There probably is that one person who knows exactly what they were going to be at 5 years old and is on it from Day 1, but rest assured you have time and resources to decide your vocation.