It seems the OP's question has already been answered, but I have a bit to add.

First off, I completely agree with allowing a dog to mature before altering. I feel that especially true of larger breeds. Though there is no medical reason to allow this (at least not that I know of), I prefer the look of a mature animal, rather than one who has grown tall and rangy as a result of the growth plates closing too late.

But I will say that sighthounds often do not come into season until later. Many sighthound bitches (especially those of the larger breeds) often go until they are 18 months to 2 years old! But other breeds can be much earlier, and for smaller breeds, 9 months is certainly not unexpected.

But no, an intact male being around a young bitch does not "push her over the edge." Instead, if there is an older bitch that is in season, sometimes that can push the younger one, but not always...