What's with adult gang bangers?

So I went to visit my parents and ended up staying all weekend (nothing like coming home). I noticed that a guy I went to high school with is still around. In school he was always gang banging and he lived down the street. So on my visit I went to the corner shop to buy some cigarettes (yes yes smoking is bad). Anyways I saw Jaime, the gang banger, he's my age, 22, but I noticed that he was arguing with some teenagers from another gang. He was literally throwing gang signs and threatening these kids. It looked so bizarre to me. And I wondered what could these kids have done to have a grown *** man and his friends fighting with them. I would like to know what your opinion is as to why gang bangers continue banging into adulthood? And why would they have confrontations with teens, even if they are from another gang, why pay attention to them?