Ah, Hindi. That's not strictly about age, though, is it? It's as much about relative social status (though age may be one factor in that). So you'd potentially

Ah, Hindi. That's not strictly about age, though, is it? It's as much about relative social status (though age may be one factor in that). So you'd potentially say आप to a younger person than yourself in order to show proper respect, e.g. if they're an important official or similar figure.