When I grew up, I would become an astronaut, a lawyer, or a teacher - just not an engineer.
If you have some more room, you might want to consider adding one or two extra professions there. Since your entire essay is centered on growing to appreciate engineering, a few extra professions would highlight your change.
Something like: I would become a doctor, a lawyer, a teacher, a race car driver, anything- just not an engineer.
Also, if you switch astronaut with something starting with a consonant, it flows more smoothly and highlights the difference between being AN engineer and being a teacher, doctor, etc.
Even though I was set on going to medical school,
Maybe change it to something like "By the time I was 12, I was set...
research opportunities, as well as, internships
You don't need the commas.