Responsa for Yevamot 213:4

אמרו להם ב"ה לבית שמאי ממאנת והיא קטנה אפילו ד' וה' פעמים אמרו להם ב"ש אין בנות ישראל הפקר אלא ממאנת וממתנת עד שתגדיל ותמאן ותנשא:

<b><i>GEMARA</i></b>. Rab Judah stated in the name of Samuel: What is Beth Shammai's reason?<span class="x" onmousemove="('comment',' For ruling that ONLY BETROTHED WOMEN MAY EXERCISE THE RIGHT OF REFUSAL and that consequently a married minor may not exercise the right. ');">⁹</span> Because no stipulation is attachable to a marriage;<span class="x" onmousemove="('comment',' And the validity of the marriage is not in any way impaired even if the condition that was attached to it was not fulfilled. The law assumes that the man tacitly renounces, on cohabitation, the condition. ');">¹⁰</span> and were a married minor to be allowed to exercise the right of refusal, it would come to be assumed<span class="x" onmousemove="('comment',' The invalidity of her marriage being assumed to be due, not to her minority, but to some unfulfilled stipulation that was attached to her marriage. ');">¹¹</span> that a stipulation is attachable to a marriage.<span class="x" onmousemove="('comment',' Even in the case of one who is of age. Hence Beth Shammai's ruling in our Mishnah. Cf. supra note 1. ');">¹²</span>

Teshuvot Maharam