After retiring seven years ago as an administrator with the New York City Housing Authority, Alvin Reinstein, who had attended Yeshiva University as a math major four decades earlier, took up Torah study. Some learning at home, some classes at his Teaneck shul.

“But there were too many interruptions,” he said.

So he decided to do it full-time. As a rabbinical student at YU. Where his son Sam was already enrolled in the ordination program.

During the school’s Chag HaSemikhah [ordination] Convocation on March 19, the Reinsteins, father-and-son, will both receive their rabbinical ordination.

While countless fathers and sons number among the more than 3,000 men that YU’s Rabbi Isaac Elchanan Theological Seminary has ordained through its 121 years,  Alvin and Sam are the first to be ordained on the same day, they said they were told by the school’s administration.

“It’s going to be amazing,” said Sam, 27, an actuary who actually received his ordination 2½ years ago but is attending the convocation this year because they are only held every few years. He serves as assistant rabbi at Congregation Kol Israel in Crown Heights. (Full disclosure: Sam Reinstein is the husband of Jewish Week staff writer Hannah Dreyfus.)

Sam, who grew up in Teaneck, said friends often turned to him for advice during school and camp, and that he decided to become a rabbi “because I want to help the Jewish people.”

Alvin, 66, said he “followed in his [son’s] footsteps” in order to foster his “spiritual growth. I’ve always enjoyed studying Talmud.”

“This celebration of RIETS musmachim [ordainees] recognizes both the enormous commitment of Torah learning and attention to personal growth demanded of each student as well as the profound and positive influence they will have on communities around the world,” Rabbi Menachem Penner, dean of the rabbinical school, said in a statement.

At YU, the Reinsteins shared some classes and sometimes learned together as chavruta partners, in a natural collaboration. “Neither of us is competitive at all,” Sam said.

If they disagree over a point of pilpul, Alvin said he concedes to his son. “He has seniority.”

Alvin said he is open to helping out at his synagogue, Congregation Beth Aaron, before he and his wife make aliyah in a few years, but “I don’t really want to have a full-time job.”

Father and son will probably mark their semicha simcha with a seudah shlishit meal at Alvin’s synagogue.

The YU convocation of more than 130 men will include honors for Rosh Yeshiva Rabbi Hershel Schachter, chairman emeritus Rabbi Julius Berman and philanthropist David Arbesfeld.

Alvin said he hopes some of his age-group peers will follow his example in the ordination program. “I’m telling everyone that it’s eminently doable if you’re retired. Why not?”