I think that gang leaders and the hierarchy tend to vary in ages between mid 20s to late 40s but most of the gang is operated by young people. Also i think that its such a violent market their involved in they need to keep their ranks filled with young blood so that they can maintain drug turf and power. Some gang leaders dont even live in the neighbourhoods that they do business in. I think to become an OG in a gang you have to last well into your thirties without getting killed.

Heres a chicago gang leader that lasted till he was 60.
http://www.suntimes.com/news/metro/9897741-418/black-disciples-leader-ran-drug-gun-trade.html

Then on the other end of that spectrum you have hybrid gangs that are entirely made up of teens.
http://www.dnainfo.com/20111104/harlem/g...s-other-weapons