My daughter does the ISTD Imperial syllabus. The pre primary Class Examinations can be taken from age 5 ( 4 children together class taken by teacher with examiner marking). The General Graded examinations can be taken from age 6 in the Primary Grade (two children dancing together, some excercises and the dance on their own).
There is a difference between the content in the syllabus between RAD and ISTD Imperial for the same grade number. We like to refer to a lovely RAD book called "Step by Step Ballet Class, An illustrated guide to the official ballet syllabus". It has excellent illustrations and easy to follow descriptions, however we have to flip from grade to grade as the content in the grades is different in RAD and Imperial ISTD as is some of the terminology eg. RAD arms in "5th position" is en-couronne" in ISTD. We have been unable to find a similar book for the ISTD syllabus.
I have no idea which is preferable, they are just different, I myself studied RAD including the majors (as they were called in my day!). For those of you who like to examine the syllabus in detail, here is the link to the ISTD syllabus, I am sure there is a similar link for the RAD, though the second link gives the guidelines on minimum age guidelines. Sorry I can't help with BBO, I did do all my BBO grades in tap, but this is now way out of date! Hope this helps....http://www.istd.org/...abusoutline.pdfhttp://www.rad.org.u...s/051graded.htm