Here are a few links of volunteer programs local to Houston:
Emily recommends the following next steps:
Very exciting that you have some ideas on what kind of career might interest you! I did not know at your age, and I happened upon Biomedical Engineering as a major in my senior year of college. Volunteering at a hospital is a great way to get a view into the health care industry in general, but don't let that be the complete picture. The job opportunities for a biomedical engineer can vary widely - both in industry (i.e. hospital, medical device company, pharmaceutical company, etc.) and in type of role (sales, clinical research, design engineering and project management).
I would also recommend trying to find some visibility into the medical device industry. Perhaps you can send a letter to some local companies and ask if anyone might be able to meet with you or let you shadow for a few hours to see what it is they actually do for work. It looks like Stryker may have a facility in that area? I know there are other companies in San Antonio and Austin if you are willing to make a drive.
Another great avenue is to get involved with SWE - Society for Women Engineers. They do a lot of outreach programs with youth in high school. https://swe.org/k-12-outreach/youth-programs/
Good luck in your search! Be bold about asking! I've never turned down anybody who asked if they can shadow me for a day :)
It's great that you're thinking about volunteering opportunities and getting out there to gain some experience! Hospitals and health clinics are great ways to get exposure to healthcare in general, which is a big part of getting experience in biomedical engineering. Houston is home to many world-renowned hospitals and I'm sure they would be receptive to your willingness to volunteer. Houston is also a great city for medical device companies. I would do some research online to understand which companies are located near you and understand what their products are. Once you find some that interest you, I would send an e-mail on the website describing who you are and what you're interested in learning or helping with.