When will my record swipe clean enough for a clean background check?

I was charged several times 17.y.o and under for numerous charges of theft, ault, GBH and traffic offenses and so forth which took place in QLD, now I'm 22 and live in NSW and want to qualify for security license (have already done course Security 1ABC) How long do you know or think will take for me to have a clear background police check?