Can you call yourself polyamorous if you have never been in a poly relationship, and are young? (I have done loads of research into it and feel it sums me up perfectly, but I am currently sitting a levels so haven’t actively looked for a relationship)

Yes. Just like you can be gay even if you’re young and have never been in a gay relationship. Focusing on your studies instead of relationships right now is mature and responsible, and I have no doubt that you will grow into a healthy, awesome, self aware practitioner of polyamory! For now, it is totally legit to identify as polyamorous even if you’re not in a poly relationship. Good luck with your exams!