Just not true. It's easy to see gangs are located generally in poor inner cities. Where are the crips and bloods? Watts, compton, Westmont. Where are they not, Beverly Hills, Laguna Beach, Malibu.
Not true again, many gangs especially MS-13 coerce kids into joining or they essentially die or a family member dies. So when you're 8 and surrounded by gang bangers who know where you live. Whatcha gonna choose? Then you get indoctrinated.