If you head to www.med.ubc.ca/admission/index.htm there is a table about midway down the page outlining courses which must be completed, at the latest, during the year which you apply to medicine.
This means that Bioc 300 is a required course, unfortunately, and would mean that any pre-requisites to Bioc 300 (if there are any), would also need to be taken for credit just to allow you to register for Bioc 300. This is why I suspect it will take you three years to do the pre-reqs, although you should really check UBC's calendar, as I might be wrong. Here was my situation at UVic:
First year: Bio 225 (the pre-req for Bioc 200)
Second year: Bioc 200 (the pre-req for Bioc 300)
Third year: Bioc 300 (and simultaneously apply to med school)
Therefore, while Bio 225, and Bioc 200 are not required by UBC Med, I still needed to take them for credit just to allow me to register for Bioc 300, which was required by UBC Med. This took me three years to accomplish.
The reason I suggest looking at the UBC calendar, is that you might be able to compress the Bioc 300 pre-reqs, into one year, so that in theory you could take Bioc 300 in your second year. This would allow you to apply to med school after two years.
To answer your second question, UBC Med states that it doesn't discriminate based on age, and I believe them. I'd guess that at least 25 students out of 120 are over 25 years of age. I believe the disparity in numbers is reflective not of bias, but rather a smaller pool of older applicants. Still, many students in my class have graduated, worked for a few years, and decided to re-enter school.
So, I'd check up the UBC calendar, and plot some timelines as to when the pre-reqs can be accomplished. You also need to have written the MCAT *before* you can apply (whereas with Bioc 300, you can be taking it simultaneously as you apply). Therefore, *if* it's possible for you to apply after two years, you'll need to write the MCAT after the first year. You should check out these time-lines for each medical school that you are interested in: I used UBC and UVic as they are the ones with which I'm most familiar.