My advice for a high school student thinking about veterinary medicine is to please, please, please keep an open mind. Don't put on blinders and only think about veterinary medicine. Take the time to explore other subjects, careers, jobs, hobbies, etc. High school is still very young to have fully decided what you want to do as an adult, take your time to be sure you are jumping into the right career for you.
I say this as someone who decided I wanted to be a veterinarian at 6-7 years old, I used to go to the library and read books to research veterinary schools, how to apply, what to do to get into veterinary school, etc. This was before computers, internet and google were big things, we had to go to the library to do research or look things up. I started volunteering at an animal shelter at 12 years old. I got my first job at 17 years old, in a veterinary clinic. I really only worked in veterinary clinics all the way through high school and undergrad. I only focused on getting experience for veterinary school. I didn't really think about anything else or any other careers. I am now a veterinarian and looking back on it all, I wish I had taken the time to explore other interests, hobbies and careers. I may very well still have ended up in veterinary medicine, but I have put myself in a box. All of my experience, volunteer work, work experience, etc is centered around animals and I am stuck as far as career goes. If I decide at any point I want to leave veterinary medicine, I have to start over, completely over, with entry level job salary, which I can't do because I have $400k in student loan debt.
Don't shove yourself into a singular box.
It is fine to get some animal experience in high school, do some volunteer work, maybe shadow a vet, but please keep your mind open. Be well-rounded, find more to do than just animal experiences and veterinary experiences. I am fairly confident the reason it took me 3 years to even be accepted to vet school is because I only focused on animal and veterinary experiences and didn't pay attention to any of the other things I enjoy that make me, me. I didn't take the time to get any other life experiences. Take the time.