It is written:1 ''You shall rise up before the hoary head and honor the face of the old man'' This ''old man'' is explained as being the Torah Sage as it is said:2 ''Gather to Me seventy men of the elders of Israel'' and concludes that certainly this depends on (them) being wise, as it is written:3 ''whom you know to be the elders of the people and officers over them'' It is therefore a positive commandment to stand up before a Torah Sage who is distinguished in his (Torah) learning even if he is not old in years and not a Rabbi. It's also a mitzvah to stand up before an old person4 that is, a seventy year old, even if he is not learned provided he is not wicked. Even with a gentile old person one should speak politely to him and give him a hand for support. (KSA 144:2)
1) Lev. 19:32.
2) Numbers 11:16.
4) lit., ''hoary (or white) haired''.