Tosefta zu Dewarim 23:2

Everyone is liable in reading the Megillah -- Kohanim, Levites, and Israelites, and freed slaves, disqualified [Kohanim], Netinim (i.e., descendants of Gibeonites), and mamzerim, eunuchs, those born sexually impotent, one wounded with crushed or severed testicles (=פצוע דכא וכרות שפכה, see Deut. 23:2), all of them are liable, and can cause others to fulfill their obligations. A hermaphrodite fulfills the obligations of his (or her) gender but not of those that are not of his (or her) gender. One who is half slave and half freedman does not cause those that are of his gender or not of his gender to fulfill their obligation. Women and slaves and minors are exempt and they do not cause others to fulfill their obligation. Said Rabbi Yehuda, when I was a child I read [the Megillah] in front of Rabbi Tarfon in Lod and he praised me. Said Rebbi, when I was a child I read [the Megillah] in front of Rabbi Yehuda in Usha, and there were elders there, and none of them said a word. They said to him, one cannot bring a proof from one (i.e., such as Rabbi Yehuda), who permitted that very thing to be done. [Nevertheless,] from that time and onward, they became accustomed to permit minors to read [the Megillah] in public.