http://adsales.wwe.com/research/
Only 15% of WWE's audience is in the 12-17 range that wouldn't be likely to know who Sting is. The largest age group (41% of viewers) is in the 18-34 range. People in the middle of that range and up would have started watching wrestling in the late 80s and early 90s and would definitely know who Sting is and care about. The younger members of the audience can be educated pretty quickly about who he is and his look is unique enough that he will grab their attention instantly.