רבי יוחנן said that an adult does not mean an actual adult - רבי יוחנן אמר לא גדול גדול ממש
Summary:
The same מחלוקת between שמואל and ר' יוחנן regarding the rule of מציאת קטן לאביו applies to the restriction of not being able to be מזכה an עירוב though a בן קטן. An אמה העבריה however can be מזכה for her master since her מציאה is hers. According to ר"י however, one cannot be מזכה the עירוב even through בנו גדול if he is סמוך על שולחן אבינו. But he can be מזכה through his בן קטן if he is not סמוך על שולחן אביו. The concern of איבה is (only) when it can lead to negative consequences, but not by a slave or a maid (and also not by a stranger). The מציאה of a daughter belongs to her father even when she is a נערה since he can hurt her by marrying her to a מנוול. A woman can be מזכה the עירוב for her husband only if her own house is included in the עירוב because of מגו דזכי לנפשה.