Why does it say "Elem (youth)"? In verse 55, he is called a "Na'ar"!
Rashi (55, citing Yevamos 76b): Doeg said, before asking if he is fit for kingship (refer to 17:55:1:1), ask if he may marry into Yisrael, for he descends from Rus the Mo'avis! Avner said, an Amoni and a Mo'avi are forbidden, but an Amonis and a Mo'avis are not! Doeg said, if so, you should forbid a Mamzer, but not a Mamzeres! Avner - the Isur of Mo'av is "because they did not go out to greet you with bread and water." This does not apply to women, for it is not normal for them to go out to greet Doeg - the men should have gone out to greet the men, and the women to greet the women! Avner was silent. Sha'ul said, "ask whose son is this ELeM" - this law NisALMah (is hidden) from you. Go ask in the Beis Midrash! 1
Malbim: When speaking to Avner, Sha'ul called him a Na'ar, which implies a youth, or one who serves or is being trained; he is still not at a high level. He told Avner to ask about the Elem, a more esteemed term, so he will be honored in people's eyes. (One who will marry the king's daughter should be respected!)
Radak citing Yevamos 77a: They answered that she is permitted. "The honor of a Bas Melech is (to stay) inside" (Tehilim 45:14; women should not go out even to greet women). We learn this from "where is your wife Sarah?" (Bereishis 18:9. It is praiseworthy that she stayed in the tent.)
