Thanks to this question I am compelled to ask:
What is the source for not eating Matzah prior to פסח?
Is there a source for not eating it for 30 days prior?
There (471:7), he quotes Sharei Knesset Hagedola brought in this answer. Interestingly, he quotes it as saying from "Rosh Hashanah", which I'm assuming in this case refers to Rosh Chodesh Nissan.
With regards to not eating Matzah 30 days prior to Pesach, there is a letter from the Lubavitcher Rebbe (published in Likutei Sichot volume 11 page 293) to a person who was told that he must remove some of his teeth for health reasons.
In the end of the letter (dated the 4th of Nissan 1954), the Rebbe writes:
And in these days, which have already started (we have already started?) the Matzah, the bread of healing (sourced here to the Zohar II:183B), which is why we are careful to refrain from eating Matzah 30 days before Pesach....
The Alter Rebbe declared: The matza of the first evening of Pesach is called the Food of Faith; the matza of the second evening is called the Food of Healing. When healing brings faith ("Thank you, G-d, for healing me") then clearly there has been illness. When faith brings healing, there is no illness to start with.
We have an obligation to start learning about the holiday 30 days before, and since the faith must proceed the healing, we spend the 30 days prior to the holiday studying the holiday but not eating the matzah, so that when we finally eat the Matzah we have made sure that we have preceded the healing with faith.
See there for more details.