I think we have never had kids under the age of 12 compete double backs in this whole country. Many of the juniors (girls born 2005-2003) didn't even do it in the Nationals this year. I would be super impressed to see a 10 year old throw that skill in a routine! It's a risky skill and can lead to a catastrophic injury, so no need to get rid of safety mats, pits and spotting too early.
I don't think the poster was talking about the USA.Kids were doing them in 2008 at JOs and they were definitely under 12...they weren't all that common and you saw double twists more often, but they were being done.