CFI
It isn't in the flight manual that it indicates that you must have 20 hours before solo, unless it is an Australian requirement/extra but a US FAA regulation.
In the US back in 1995 there was a FAA regulation by the name of SFAR 73 in which it states <<A person who does not hold a rotorcraft category and helicopter class
rating must have had at least 20 hours of dual instruction in a Robinson R-22
helicopter prior to operating it in solo flight.>>
Should you which to read the whole regulation it can be found at
http://www.faa.gov/avr/AFS/FARS/far-61.txt and a short way down the page.
This is what is probably being stated to you and by the sounds of what your instructor is telling you it is also an Australian requirement.
