I found this on the LCMS. It talks more about their position on intelligent design than it does creation (young earth/old earth/gap/theistic evolution).
http://lcms.org/Document.fdoc?src=lcm&id=1103
From the LCMS website:
Of Creation
(St. Louis: Concordia Publishing House, N.D.)
[Adopted 1932]
5. We teach that God has created heaven and earth, and that in the manner and in the space of time recorded in the Holy Scriptures, especially Gen. 1 and 2, namely, by His almighty creative word, and in six days. We reject every doctrine which denies or limits the work of creation as taught in Scripture. In our days it is denied or limited by those who assert, ostensibly in deference to science, that the world came into existence through a process of evolution; that is, that it has, in immense periods of time, developed more or less of itself. Since no man was present when it pleased God to create the world, we must look for a reliable account of creation to God's own record, found in God's own book, the Bible. We accept God's own record with full confidence and confess with Luther's Catechism: "I believe that God has made me and all creatures."
Also this...
Was the universe created in six literal 24-hour periods?
Q: A person, because of his study of science, does not believe that the universe was created in six literal 24-hour periods. Does this fact, by itself, render this person ineligible for membership in the LCMS?
A: A person's private views regarding this question do not automatically disqualify a person from becoming a member of the congregation. It is possible, of course, that someone holding to a given theory about the "six days" of the creation accounts also holds to views about the Bible that would be troublesome and perhaps in some cases detrimental to saving faith.
But judgments in this regard belong in the realm of individual pastoral care, and are not a matter of hard and fast rules so that someone's personal opinions in this area would become in effect a kind of litmus test for membership.
It has generally been taught in our church that unless there is a compelling reason, on the basis of the biblical texts themselves, to understand the six days of the Genesis accounts as anything other than normal 24-hour days, we are to believe that God created the world in six 24-hour days (see Luther's Small Catechism with Explanation, Question 97 [CPH, 1986, p. 106]).
Official members of the LCMS (congregations, pastors, rostered church workers), of course, pledge to honor and uphold the official position of the Synod on doctrinal issues, including its official position on creation.