1. The Torah (Vayikra 19:32) says, “Mipnei Seiva Takum V’Hadarta Bifnei Zakein.” This verse teaches that one must stand before our elders and talmidei chachamim. The Shulchan Aruch (Y.D. 244:1) rules that one must stand for elders once they have reached the age of seventy. Therefore, if elders are walking down the aisle and they are above the age of seventy, all those present must stand up before them.
2. If one does not know the exact age of the elderly person he must stand in accordance with the rule of sfeika d’oraysa l’chumra, one must be strict when a doubt arises involving Biblical law. (See Yechava Daas 3:70)
3. The poskim debate whether one must stand before an elderly woman. (See Sefer Chassidim 578 and commentary of the Chida and Shevet Halevi 2:114)
4. The Shulchan Aruch rules that as soon as the elderly person or talmid chacham has passed by, one is permitted to sit down.
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