Well, YOU may not teach that...but it's been taught in the LDS church! LDS general authorities and writers have called Lucifer the "next heir to Jesus Christ" and "a spirit brother of ours." Furthermore, they labeled Jesus as an "elder brother" to Lucifer. (documentation all follows)
So, do you want to explain how Lucifer can be the "next heir to Jesus" and not be your "elder brother?" The way you phrase your objections, you do not object to the fact that you believe that Lucifer is your brother, only that he is not your elder brother.
But if Lucifer was spirit-birthed in heaven before you and every other Mormon, alive or dead, why bother insisting on these "technical" objections?
The bottom line here is that according to LDS teachings, both Lucifer and every Mormon claims Jesus as their "elder brother." Wow! What a family!
Documentation
In 1844, LDS author W.W. Phelps wrote: "And again, we exclaim, O Mormonism! No wonder that Lucifer, son of the morning, the next heir to Jesus Christ, our eldest brother, should fight so hard against his brethren; he lost the glory, the honor, power, and dominion of a God and the knowledge, spirit, authority and keys of the priesthood of the son of God!"
By 1949, according to this LDS Conference Report, LDS apostle Joseph F. Merrill says that Lucifer "is a spirit brother of ours and of our Lord Jesus Christ..." Here's the exact quote:
"Now there is another personality of which I desire to speak, ... that person is Satan, the Devil. But according to our understanding and teaching, Satan is a person with a spirit body, in form like that of all other men. He is a spirit brother of ours and of our Lord Jesus Christ, who is our Elder Brother in the spirit world. The earth was in course of development for the abode of man in mortality. A Redeemer was to be sent down and make it possible for the Father's children to return to him." (LDS Conference Report, April 1949, p. 27)
LDS Apostle John A. Widtsoe taught that Jesus is not only the brother of Jesus, but his "elder brother." Exact quote:
"The story of Lucifer is the most terrible example of such apostasy. ... He pitted his own plan and will against the purposes of God. He strove to gain the birthright of his Elder Brother, Jesus the Christ." (Evidences and Reconciliations, p. 209)
Syllogism: http://dictionary.reference.com/browse/Syllogism
A: Christ is our older brother
B: Lucifer was right up in the kingdom and didnt like being second fiddle to Jesus. (merit, not age is important)
C: No logical deduction for the age of Lucifer can be made from these two pieces of information, but you cant tell his age from this.
Is he our brother, yes, is he a good guy (your kidding right?), was he rebellious? absolutely
but is he my elder brother? WE DONT KNOW!