| Developmentally, older people are definitely the people younger people want to and probably should try to be like. Even a couple years of age difference can be appealing. It's even better if the older person is able to be sociable/has good social skills and if they also have good boundaries. If the older person is mostly stable personality-wise and able to be dependable, that too is another drawing point. That's something that is developmentally normal. It's also why children and even older 'minors' are vulnerable to adults in a general sense. If people really like someone in their life, then interacting with or seeing that one person can be a major highlight of their day. They may not be 'obssessed' or too anxious, but they still (especially very young kids) will bounce around like you're the greatest thing since sliced bread. That's a developmental thing, they will probably grow out of it, but one hopes they retain enough that they can be honest about liking and acting like they like people when they are older even if they don't jump out of their own skins anymore. People usually say 'hi' as a simple social thing. In some ways it's a social skill. People reinforce for themselves who they know, and who they recognize and they can be sociable enough to acknowledge a recognized person's existence. It's usually not dependent on age grouping so much as whether they personally like you, or just recognize you and want to be polite. The problem is that you can't stop other people's behavior and they have as much right to their thoughts and feelings and behavior and developmental stages as you have to yours. As an aside, the younger people also are more at the mercy of their development and they can't help being interested in and wanting to be accepted by 'older people.' You are an 'older people' and that's that. The other problem with the 'hi' stuff is that you can growl at people who are polite, but older or younger that's a good way to end up alienated from everyone; or with all kinds of unexpected bad consequences. (You can say 'hi' or look at them briefly and smile, or sort of wave or offer some other acknowledgement of their gesture and keep on your way. You aren't obligated to stop and chat if you don't want to. It is in your best interest to acknowledge the gesture though mainly because it helps them feel better, and that eventually circles back around and makes things easier for you later. Minimally, those younger people have adults in their lives who will act as their advocates if the kids feel hurt or otherwise slighted.) part of it's developmental, another part of it will be personality-based (some kids just will like some older teens more than others, the same way older people just have personality issues sometimes for good or ill); it's really challenging for adolescents too because usually that's a time where those people are developmentally primed to be 'independent' and it may be hard to feel independent when also feeling beholden to younger children (adolescents usually want to spend time with their age peers or older people too, and not so much time with younger people) try to cut everyone some slack including yourself | 
