I don't think its a courteous language to use when approaching elders. Especially "hi" seems more of a slang unlike "hello". " Good evening, good morning, good afternoon" are the right kind of greetings we ought to use towards the elderly. The good thing with the curriculum in my country, it tackles all through from kindergarten upto a certain level so that the child grows knowing how use etiquette esoevit greeting.
The moment you great an elder person, "hi" a lot of things start lingering their mind. Some of them will obviously think you're spoilt and don't know the right language to use. This might even spoil your reputation as person especially if you're that kind of a person who seems to care a lot. Besides, they might even think that you're not learned. Even such a simple thing you don't know how it should be.
Courtesy will never cost us anything, let's uphold respect for the elders.