Age doesn't matter. Worth knowing that a pretty standard trajectory for PMs is: graduate CS at 22, work in the industry for 3-4 years, go to B-school, graduate at ~28-29, start out of college as a PM. So you're kind of right in the range.
I can't imagine how a certification would matter, but I transitioned to PM in the same company instead of applying cold, and I was hired (for both roles) in part because I had a reputation in the field I was in. I doubt very much that you'd learn anything from the certification (or, for that matter, from business school) that would help you do that job.
I could write a pretty decent list of hazards for engineers moving to the business side of technology companies. But for a PM, probably the most important one is: product managers aren't project managers and they're not engineering managers. You have to simultaneously let go of what's happening in the repository while not letting go of the MRD/feature-function-benefits. I found that to be a pretty nasty tightrope walk and didn't handle it well.
I left Arbor in 2005, so my advice is pre-YC-era, and a lot has changed at startups (though less so at enterprise software companies!). Every role I've had since has been entrepreneurial, so while I'd say that I use skills I developed (haphazardly) as a PM, I haven't had a formal PM role since.