About your age concern.
I'm 45 years old, and I'm not the oldest PhD student at my school. I also read a lot about age preference before applying to a PhD, and I was afraid of that. But now that I'm a PhD student, I really don't think that age is usually a problem. Of course there should be some schools that are like that, but generally speaking I don't think age should be a concern.
The problem is often related to other factors, that have some correlation with age. For example, it will be harder for you to explain why you would give up on a successful career in industry to become a PhD student. You are probably used to standards in life that are quite better when compared to PhD students'.
Like, it is harder to convince someone I'm passionate about research at 45. After all, they may think: "If he likes academic research that much, why did he wait until he is 45 years old to apply? Maybe he is just thinking doing a PhD is easier than getting a job. Maybe he just wants to move to the US". So, in this case, they are not worried about age, they are worried about my motivations to do a PhD.
So, to me, age is not the problem. But age is related to experience, motivation, and other factors that can be a problem if you can't explain them, or if they do not make sense to schools. Given your profile, your motivation should be different from what schools hear from those in the 20s, So, your strategy should also be different. If an applicant is in the 20s, has no teaching experience, and no research experience, they can still convince schools that they just didn't have time for that yet, but that´s something that they are changing now. But you are in the late 30s. You had time for that kind of thing if you really wanted to. But, somehow, you never did any teaching or academic research, and now you want to convince someone you are willing to give up a good job in industry to live the hard life of a PhD student, doing something you've never done before, and committing yourself to do that for the rest of your career. It's not an easy sell, right?
If you work on those other factors, age shouldn't be a concern.
About your other concerns you mentioned.
You wrote that you just recently completed your MBA. It looks like you already may have missed an opportunity there, since it's often easier to get involved somehow with research during a PhD than now. Yeah, it can help a lot if you work with a professor to get some academic research experience. And I see students getting closer to professors during MBAs to do exactly that, improving their chances of getting accepted to a PhD later (due to different factors, like some research experience to show, some research paper to attach to the application, a stronger letter of recommendation).
Your profile so far seems a little weird to me too. Maybe it's ok, and I just don't have the information. But I think you need to do some work about what you want, what are your goals, how you are presenting yourself. Some examples:
- You wrote that one of your areas of interest is Marketing - Consumer Behavior. When I see someone applying to Consumer Behavior, a common expectation I have is to see things related to fields like psychology or sociology. And I don't see anything that shows why Consumer Behavior would be your research area.
- Every time I see a list of schools like yours (Harvard, MIT, Stanford, etc.), I get the feeling that not much work has been done on school selection. Research fit, for example, is usually one of the most important things to take into consideration when choosing schools, and we don't expect Harvard, MIT, and Stanford to have the same kind of research fit. If you fit very well in one of them, you probably do not fit well in at least some other one. This looks like a list of famous schools, not a list of schools that follows a good strategy to apply.
- You didn't even really answer what made you pursue a PhD. You just mentioned some topics of interest, but not what you made you pursue a PhD.
- Planning to apply to only 5-6 universities? That seems very low for PhD applications. I usually see at least 10, often around 15.
- You wrote that you are "aware" of a few research topics. You sure need to be more than just "aware". You should ideally know what those topics are, how those topics are covered in academic research, who are some of the main professors and universities that work on that topic, what are the challenges people face regarding that topic, what are the methods used, how can you expect to make a contribution. You don't need to know everything, of course. But right now it sounds like you have no idea what you are getting into.
So, right now things don't look good. Coming from industry. Applying to few schools, just top ones, probably without a good research fit. No research experience. No clear motivation. No mention about the quality of your letters of recommendation. No GMAT yet. A lot of writing about work experience, that often doesn't matter that much for PhD applications.
But you still have time, you are not applying now. If you really want to go for a PhD, you work hard to improve your profile, and then things should look a lot better.