Rabbi Shlomo Yosef Zevin, according to here was given smicha by the Aruch HaShulchan. Assuming that the Aruch HaShulchan ordained Rabbi Zevin at the very end of his life, Rabbi Zevin would have been no more than 9 years old. Was this indeed the case, and is it indeed possible for someone under the age of Bar Mitzvah to become ordained as a Rabbi?
The Aruch Hashulchan died in 1908 (source, see footnote 9), and according to the article you brought, Rav Zevin was born somewhere between 1886-1888 (in fact, it was 1888). Therefore, he could have received Semicha from the Aruch Hashulchan when he was in his late teens or early 20s.