Q. Does one have to stand for an elderly if one is unsure of his age?
A. If one is unsure if an elderly has reached seventy, Yabia Omer (Y. D. 3: 13), Yehave Daas (3: 70 ) rules that since this is a Biblical mitzva you have to be stringent when in doubt and stand.
Ayeles Hashachar (Vayikra) quoting Chazon Ish maintains that if one has a sofek if an individual is a talmid chacham or not, one can rely on the fact that the majority of people are not. However, if one is in doubt if the elder is sixty and he usually stands for them, when in doubt he does not have to be stringent.
Horav Shlomo Miller’s Shlit’a opinion following his answer above in regards to elders today, is that in doubt he should rise slightly.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a.