Don't listen to the clearly salty pre-med. We all start somewhere on how much we know about the process.
When you take the MCAT is really dependent on how prepared you feel for taking an 8 hour long test that covers a good chunk of what you've learned in school. Traditionally, most people take the MCAT the spring/summer of their junior year, and apply to medical school during their senior year so that they start med school right away. If you do that, you want to have all of your mandatory pre-med classes done before your MCAT. Some people opt to take it during what's called a "gap year" which is after you graduate university.
Volunteering and extracurricular stuff should be both relevant to clinical stuff and stuff YOU enjoy, which can be outside of medicine (like hospital volunteer work, community outreach projects, habitat for humanity, pre-med honor societies, etc etc). Shadowing is a good way to network with physicians, and you should try to shadow a few different types of doctors to see what you like/don't like and see medicine from different perspectives. Just keep a log on your computer of what you do, how long you do it, and stuff about what you did -- like a resume of sorts -- so you have that information for when you do apply to med school.
As a current med student who was completely clueless about the process when I started (first gen doc in my family), the best advice I could give is to tell you to take it one day at a time and never compare yourself to others in a negative way.
