Heather, your axies wil breed when they are sexually mature and when the inclination takes them.
But the rate at which they mature will vary from animal to animal. If you leave then together your probably going to wake up to eggs one morning, anyway.
If you are at all worried about it then put a tank divider in or keep them apart. Until you think she's ready...It's quite likely she will breed some time between 8 mths and 12 mths. If left to their own devices it's also probable you they won't breed until December thru to July.
Sorry no absolute answer...as for the stress thing I have heard same about dog breeding, 'don't breed on first season she's too young'. Another arguement says if she's capable then she's ready. Personally i think if the female is mated too frequently then she will suffer and that after mating she should be left to recover for a a couple of months. But in the their natural habitat and axie might breed 3 times in the due season.
