Are being +30 and having a Ph.D. considered as barriers to become an air traffic controller in NAV CANADA? The requirements to apply to the training phase of NAV CANADA (to become an air traffic controller) are listed here, in which no upper bound corresponding to the age and the education level of a potential applicant is noted.

Does that mean an over-30 Ph.D.-holding person has also chance to be picked for such position (or he may be pruned off the list of successful candidates because of being old and over-qualified)?

PS. Any potential similar piece of knowledge associated with other aviation control bodies is also appreciated.
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.