Will medical institutions reject an applicant based on being 28 years of age? As I've contemplated the future over the past year, I have returned over and over again to the idea of becoming a doctor -- specifically, a neurosurgeon. However, I recognize that as a 28 year old Physics BS who would need to take a year of postbac courses before even applying to medical school, I might face unreasonable challenges should I choose to pursue this goal. I recognize that by the time I would be ready to apply, I would be 7 to 8 years older than the typical medical school applicant. My main fear is the idea of getting partway down the road to becoming a doctor and then being unanimously rejected by the institutions (schools, residency programs, employers, etc.) based on my age, rendering my efforts fruitless. Is this a likely outcome?
In the US, being 28, 30, or even 40 is not a problem for getting into med school. I was 26 when I was admitted, and I was far from the oldest in my class. In fact, by my senior year, they had admitted a couple of students older than my current age at the time! If you haven't been slacking off in between college and now, it could make you even more competitive because you can point to past successes and have interesting stories for the interviewing process. A typical medical school in the US could easily fill each class with biology and chemistry students fresh out of college with high GPA's and MCAT scores. Someone older might have all of those, plus the strengths of a rigorous career or valuable experience outside of medicine. You can differentiate yourself from the rest of the pool. 

Now, to the main issue of age. By the time you finish the pre-reqs, ace the MCATs, and finish 4 grueling years of medical school, do you think you'll have the energy or motivation to do an even more intense additional 7 years of neurosurgery? Neurosurgery is competitive enough that they can pick whatever candidate they want. While not a given, you will likely face some "soft" age discrimination for intense/competitive residencies and fellowships. For this stage, you'll have to work extra hard to convince them you can physically compete with the youngin's, much less complete/survive the program. Once you finish your neurosurg training, you won't have problems finding a job. Once you're board eligible/certified, no hospital cares what school you went to, how old you are (to a point), or what you did in the past. All that matters is what you can do for them, ie increase billing by a zillion dollars.    

You can get more detailed responses and support from the forums.studentdoctor.net website. There's even a sub-forum for the "non-traditional" applicant, which honestly, isn't so non-traditional anymore!