I think you have around 1-2 years for them to mature.
But put it this way. Assuming the person you bought them from did not purposely pick on or the other you have a 50% chance either way.
So to have 3 females/ 3 males it would be a 50% chance either way:
Male and Male and Male = 50%X50%x50% = 12.5% chance
Female and Female and Female=50%X50%x50% = 12.5% chance
So the chance of them being all one sex or another is 12.5%+12.5%=25%
So you have a probability of 75% that you will have both, so chance is in you favour
