A double-major in computer-science and accounting, while enrolled at an Ivy League college known as a feeder to Wall Street 
I’m being facetious. The point is doors start closing as you get older. It isn’t impossible to change direction but the more time that goes by the more difficult it gets.
So lets start at the beginning. What is it that let you decide at age 17 this is the best career for you? I don’t think it is thru volunteer experience, so what other exposure to the field and what it entails do you have?
Second, you’ll find out your 1st year in college how well you’re doing in the premed classes. If you aren’t doing well in chem, math, etc. then getting admitted to med school starts to become improbable, so you’ll know well in time to switch to another field. Engineering might not be possible at most schools (hard to change into that major) but then again if you’re not doing well in basic math/science its probably not a good fit anyway.