college courses

hi! i’m currently studying abroad for college/ sixth form after moving from manchester 3 years ago. i wanted to move back to the UK for college and live with my grandparents to do a veterinary nursing course but my parents wouldn’t allow it as they wanted me to do a levels instead. i’ll be moving back next summer once i’ve finished my a levels and i’m wondering whether i can can redo college in my preferred course and then go into uni or go straight into uni with a levels that don’t match up to anything remotely related to veterinary. can i do this? or will it not be allowed as i’ll be 18? thankyou!