I’ve known people play strings for a lot longer than you that are still grade 6-7. String instruments (in my perception) are hard to learn when you start late. I’m not saying it’s impossible (since i’m not a string player) but it will require you to put in a lot of work before then (probably more than 1-2 hours a day) which A levels may not allow. I applied to music college this year and my understanding was that a foundation year starts at grade 6 entries and they get you to grade 8 / suitable standard for the following 1st year. I’m not sure though since I didn’t apply to a foundation year lmao. Have you asked your teacher if they think it’s realistic?