Young people aren’t angry? They look quite upset to (old) me, and rightfully so. I probably would be a lot more than they are, to be honest.

One remark, maybe:

The few old people around you does not represent a valid statistical sample for ‘old people’ in general. You need a lot more data.

No offense intended, maybe it’s like that because you’re living in a family that is keen on hating and insulting one another? The only thing I would feel ok to conclude from that is they may very well be dickheads, every single one of them, but that doesn’t mean all people their age are the same. Don’t generalize ;)

To help you realize how… too fast such conclusions can be made, and no doubt how wrong they can be, consider this simple observation one may want to make reading your question:

The only constant in your interactions with older people is yourself. How come you may ask? Well, they’re all different (old) people that don’t share the exact same age, sex and personality (taste and preferences), maybe they don’t even live all at the same place. Meanwhile, you’re the exact same person. You do not change and you’re not different, they are. So, if every single one of those different and older persons you meet is hating on you shouldn’t I conclude that you’re the most likely cause of their hate?

See how easy it is to come to some nutty conclusion out of mere ‘observations’?

To be perfectly clear, I 'm not saying it’s you that’s causing anything. Far from it. First, for the simple reason that I never met you and then because you probably are not the cause of anything here. Like I said, there is not enough data to conclude anything. Still it’s so easy to conclude that it’s your fault and from there that if it’s your fault it’s all younger people’s fault—it’s not ;)

To share my own personal experience, as a child (I was young, once) I knew very early on my mother hated my guts. I started by wondering why adults where such assholes towards kids up until I realized that was not ‘all adults’ nor ‘all mothers’, it was her. That unique person she was for reasons that were her own that certainly would not allow me or anyone else to generalize her behavior to all mothers.

All of that to say there could be a lot of reasons and factors unrelated to their age.

every grandparent or elderly relative always have insulting remarks about me

I have been young myself (promise I really was, and one day you will be old too) and my grand-parents never insulted me. Not once. And as an older person myself nowadays I tend to not insult… not too often ;)