You sound very accomplished and should be proud of your skills!! Hopefully you have fun with gymnastics too. There really isn't an average though because average is all relative to who you are being compared to and there's so many possible variables here (think team vs not on team; been in lessons for 4 years vs none at all...that kind of thing). Gymnastics is individualistic and advancement and accomplishment in the sport looks different for everyone.
There is no average age. It happens at vastly different ages depending on so many factors like age started gymnastics, hours trained, type of program, the prerequisites your gym requires before learning the skill, natural skill etc.