It’s not my field, so I’m not sure. But: maths for sure, as all engineering needs that, and physics. After that, you might consider whether you want to work on the structures of craft, or on avionics. For the latter, maybe aim towards electronic engineering? Also, materials science is important in aerospace, so chemistry might be relevant.
Going forward, you could either try to get into the field after university…OR you could contact an aeropsace firm and see if they offer apprenticeships. If you became an apprentice, you might be allowed time to get a university degree while in your job.