i have a couple of comments on this from personal experience.
first, i was a junior hospital volunteer for one summer at a pediatric hospital when i was 14 years old. so-so experience.
second, when i was a junior in college i found out about a 6-week summer program for pre-med minorities at several of the Texas medical schools. i did the program at the medical center in Houston. we rotated through several different services, dissected cadavers, visited with lots of professors, had some social times. awesome experience.
i would suggest that you speak with the Health Professions advisor at your college. they should be aware of programs such as this.