Q. I heard that its a mitzvah from the Torah to stand up FULLY when a frum Jew over 70 years old (60 according to Kabalah) comes into your 4 Amot.
A. Shulchan Aruch (244: 1) rules that the mitzva of rising before a "seiva" (Vaikra 19: 32), applies to a seventy year old elderly, even if he is an "am haaretz" or ignoramus individual, as long as he is not a "rosho," when he enters your four amos (two meters) space.
Most Poskim follow the ruling of the Shulcha Aruch, and maintain that the age of a seiva is seventy years (Hagr'a on S.A. ibid quoting Mishna Avos 5: 23), Rosh on Kiddushin 33a, Shoel U’meishiv 3, 1-110, Minchas Chinuch 257:9 and Ben Ish Chai, Ki-Szeitzei. Bartenura and others relate it with the pasuk in Divrei HaYamim (1: 29: 28): And he (King David) died “BeSeiva Tova” (in a good old age), and we know that King David lived for 70 years.
However, The Rashbatz (in Magen Avos - Kiddushin 5:21), cites a Targum Unkelus that the age is actually sixty years old. The Minchas Chinuch (#407) writes that one should, in fact, be stringent and arise for someone who is sixty years old. The AriZal in Shaar HaMitzvos on Parshas Kedoshim is also of the opinion that the correct age is sixty.
What exactly the word "seiva" means is debatable, The Hirsh Chumash translation is "Stand up before a hoary head." He bases his interpretation on the pasuk (Iyov 41: 24) describing the swim of the leviathan "He makes a path shine after him; he considers the deep to be hoary," as the white foam that follows the wake he creates. The Complete Jewish Bible (Chabad.org) translates it as "a venerable person." most others have it as the aged or elderly.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a