Hello,
I don't think that your young age will be a liability in your application. Some top schools (most notably HBS) have evolved towards preferring younger applicants over the past ten years, putting you in the "sweet spot" in their eyes if you apply this coming year. Schools like Kellogg and Columbia still admit classes that are are slightly older (by a year, if you're looking at the mean of the whole class), but even for them, it's not like you're a 21-year-old kid with no experience. So, I think that you're applying at the right time. At worst, you will be able to reapply next year, and still not be "too old" then.
Re: EC activities, what really matters more than the no. of hours you put in is how passionate you are about the cause, what it tells admissions officers about you, and how much of an impact you're having on the cause. So, quality is what matters there, way more than quantity.
We wrote more about this on our blog recently:
https://blog.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/12/wha ... about.htmlOverall, I think you're competitive at a top-10 program. Depending on what you want to do post-business school, maybe add one or two more schools to the mix, although I recommend applying to no more than 4 or 5 (absolute max) schools in a given round.
Good luck!
Scott