Halacha imposes several qualifications that should be met by the one selected for the honor of leading the services on the Yamim Nora'im (High Holidays). A congregation should preferably choose for this role a married man who is at least thirty years of age. Some scholars explain this requirement based on the view that "old age" sets in at the age of sixty, and thus at age thirty a person has reached the halfway point of his youthful life. At this point, he becomes more humbled and subdued, as required of one who leads the High Holiday services. According to other opinions, a man becomes qualified to lead the prayer service already at the age of twenty-five, the age at which the Levi'im would begin serving in the Bet Ha'mikdash.
There is an additional preference that the Chazan be somebody who devotes his life to Torah study. A single man younger than age thirty who devotes himself to Torah learning takes precedence over an older, married man who does not devote his life to Torah study. Of course, the preferred candidate is a man who meets all these qualifications, meaning, who devotes his life to Torah learning, is married, and is at least thirty years of age.
The most important requirement, however, is that the Chazan is accepted by the congregation. If a congregation does not, for whatever reason, approve of a person's candidacy for the role of Chazan, then neither he nor anybody else may insist that he serve as Chazan, regardless of his credentials. Even if he is exceedingly pious and a very talented cantor, he may not lead the services without the general consent of the congregation.
The Mishna Berura (commentary to the Shulchan Aruch by Rabbi Yisrael Meir Kagan, the "Chafetz Chayim," Lithuania, 1835-1933) writes that a person who took another Jew to a secular court, without first consulting the Bet Din (Rabbinical court), is unfit to lead the services on the Yamim Nora'im. And, according to the Chid"a (Rabbi Chayim Yosef David Azulai, Israel, 1724-1806), somebody who does not regularly attend the synagogue services throughout the year may not serve as Chazan on the Yamim Nora'im. Such a person should not be chosen to blow the Shofar in the synagogue, either. Only those who participate in the Minyanim throughout the year on a regular basis are qualified to lead the High Holiday services and blow the Shofar.
Summary: Ideally, the Chazan leading the High Holiday services should be somebody who devote his life to Torah, and who is married and at least thirty years of age. A younger, unmarried man who devotes his life to Torah study takes precedence over a married, older man who does not devote his life to Torah. Nobody should serve as Chazan on the High Holidays without the congregation's general approval. A person who sued another Jew in a secular court without authorization from the Rabbinical court, and somebody who did not regularly attend synagogue services during the year, may not serve as Chazan during the Yamim Nora'im.
