Double backs seems more impressive that twisting. But it really isn't. They are equally difficult.
My daughter competed double backs as a Level 9. She just turned 11. It might have been introduced to her two summers before L9 but really only trained it the summer before L9. My daughter to this day, her fifth year in L10 struggles with twisting. She can't get past 1 1/2.
When you say "acquire a skill", does that mean competition ready or landing it once or twice? I don't consider the acquisition of a skill as a lucky landing or two and anything other than it being competition ready. Additionally, how often a gymnast trains the skill is a huge factor. Someone may get it at 9 years old but has been training it religiously for two years. Another gymnast may have gotten it at 12 because it was only being trained sporadically even though it may have been introduced two or even 3 years prior. My point is, talent is only one of the factor in acquiring a difficult skill. Additionally double backs is not required skill at any level. So some may never have it.