Hasidic Belief about the Generational Messiah

I was on wikipedia doing research on the Jewish beliefs about the messiah and found something very interesting. Apparently, the hasidic belief is that there is a person born each generation with the potential to become Messiah. This candidate is known as the Tzadik Ha-Dor, and if he ‘qualifies’ then he becomes the Tzadik Emet (Messiah).

This is all the information I could find about this belief, and I’d like to know more details. If any of you are familiar with it, I would appreciate some more information, link to primary sources, or, preferably, answers to my questions below:

Here are my questions:

1) Is the Tzadik Ha-Dor chosen at birth, or a young age, or is he selected from a pool of potential candidates later in development (like 18-25) because he shows the most outstanding potential?

2) How does the chosen candidate qualify to become the Messiah? Is he “elected” by the Jewish leaders at the time?

3) Since there is a candidate every generation, could there, theoretically, be a 30 year old and 60 year old Tzadik Emet both alive and ruling as Messiah simultaneously?