R' Shteinman writes in his sefer Ayeles haShachar on Chumash regarding the mitzvah of standing for an elderly or wise person that 1) if one has a safeik if a person is 70 years old (the age at which one is considered elderly and must be stood for) or not one must treat this like any other safeik d'oraysa and perform the mitzvah; 2) if one has a safeik whether an individual is a talmid chacham and must be stood for or not one can rely on the fact that rov people are not talmidei chachamim (quoted in the name of Chazon Ish).
R' Ovadya Yosef has a long footnote in Yechaveh Da'at (III:70) where he addresses both of these questions in greater detail. Regarding the first point R' Ovadya notes that it could be argued that a person has a chazakah of not being old until proven otherwise -- e.g. Tosfos (Yevamos 68) writes with respect to a safeik whether a boy is 9 years old and capable of bi'ah or not that there is a chezkas katnus in addition to the chezkas kashrus of the woman which must be factored into the question. Achronim debate this issue at length, as a person ages by the minute -- is a chazakah he'asuya l'histanos, a situation constantly undergoing change, classifiable as a chazakah?
The same question may be raised regarding the second point as well. No one is born a talmid chacham, and it may be said that we all start with a chazakah of ignorance. Hopefully that situation is asuya l'hishtanos as we grow in learning throughout our lives.