מילון על יבמות 124:13

1. Laws of the Mitzvah etc. - [For reference, see] the Talmud - Yevamos 62, the Rambam - Laws of Marriage, Chapter 15, and the Shulchan Aruch Even HaEzer Seif (chapter) 1. The time of the mitzvah [i.e. when one is obligated] is from the age of 18, and one who proceeds [i.e. fulfills earlier than 18] is praiseworthy. [For reference] in regards to being involved in Torah studies [i.e. as potentially delaying one's fulfillment of the mitzvah] see in the aforementioned Rambam and the Maggid Mishnah [on the Rambam]. It is not necessary [to detail the laws regarding] the matter that is explicit in the Shulchan Aruch and Later Sages (Acharonim); however, there are some ideas and opinions to note with the help of Hashem.