Do you have anything for leadership?
For you it will be important for your application to reflect your maturity. Aside from the traditional extracurriculars, let your application reveal your diverse interests in, and dedication to, maybe sports, the arts, whatever you've been heavily involved in that you do for fun, possibly travel experiences. Be sure that you show something where you've taken responsibility. Teaching/mentoring is also good and you have that. When you volunteered in the ENT clinic, how did you interact with patients? Did your research also involve patient interaction? Be sure you specify that. Did you shadow three types of doctors? Variety is good. If you have time before you apply, consider some volunteer or paid time in a non-clinic situation: hospital, nursing home, hospice, etc.
I was young, too, when I applied, and my age was never brought up as an issue. If you present yourself well and your application speaks for you, there is no reason for your age to concern adcomms.