When a person enters upon other people, does he greet the oldest  first or the youngest?
Question

                When I enter upon people and I want to greet them, do I start with the oldest or the youngest?
Praise be to Allah.This is an issue which some people do not understand. When 
  you meet someone or you enter upon someone and you want to greet them (by shaking 
  hands) or by offering tea or coffee, then you should start with the oldest, 
  because the Prophet 
  
  (peace and blessings of Allaah be upon him) had a miswaak (tooth-stick) in his 
  hand and there were two men in front of him. The younger man wanted to take 
  it, but he said to him, “The older, the older.”  
This is different to when there is a young man 
  on one’s right and an old man on one’s left, and one is sitting 
  between them. In that case one should start on the right, even though that man 
  is younger.  
On this basis, when a person enters a gathering, he should start with the oldest, but if he wants to give something, then he should start with whoever is on his right, not on the right of the oldest.