Are being +30 and having a Ph.D. considered as barriers to become an air traffic controller in NAV CANADA?
As a general answer (not pertaining just to Canada): any aspiring air traffic controller is very thoroughly tested before acceptance to a training program. Having any kind of previous education has little effect, say, higher academic merits, in my experience, may only represent someone's ability to function in academia.

Being a doctor of this or that certainly is not bad, but if an applicant holds many different credentials, it usually is, if not a red flag, a signal of the person's tendency to like studying more than doing.

ATC work is very demanding, and it requires a specific type of person: calm, focussed, extremely high tolerance to stress to mention some traits, etc. It is not a profession that I would recommend at first hand to anyone.

Regarding age, well, 50 is +30, so a bit vague definition there. If one is closer to 30, probably not a problem. Closer to 40, things are getting increasingly difficult. Thing with age limitation, or the lack of one is that declaring that age is not a limiting factor might be a politically dictated statement. Legislation probably demands that age cannot be a limiting factor when hiring people.