I'm afraid to become more and more resentful as I grow older actually.
It's not so much that I feel bitter towards the past (my childhood was good, my teenage years and up till now hasn't), I feel bitter about other people who don't realize how fortunate they are, how easy life is for them, who didn't have to struggle and who will never have to.
It's not fair to feel that way but I can't help it.

I'm sorry you feel that way. It can be a vicious poison because it detracts you from actually changing things, improving your life. But it's human.