A 5 year old boy could do back handsprings thats telling me that its better to learn at a young age before your body and brain are developed and your so small that its easier to bend back and flip.
If they kept being atheletic like doing strecthes and running exercising,then they would be able to keep doing backflips even if they got older and more developed cause they had gotten used to doing them as children so they never had any fear.
I cannot do a backflip,I am slim and I dont have any fear but I cant do a backflip or back handpring but I can do a frontflip with no hands which I learned at age 8.
I never knew what a backflip was until I was 8 and saw another boy doing one and I tried but I couldnt do one,I guess I already had bad habits in me and me body,I wish I could have learned it at 4 years old even though I never knew what it was.
Its easy if you learned it as a young child cause at 5 you dont have much fear but not every 5 year old has heard of a backflip.