There are no laws governing the age of consent when it comes to ackies. I would suggest you follow your own moral code on this issue unless it involves you and the ackie in which case I would suggest you think about it before starting a relationship as there may be provisions in the criminal code in your state for such things...
Once they start to approach a year you can get a good idea, but it depends on the individual (both person and ackie). There are a few threads around about sexing them, I've posted about it here.