They are they who...are sealed by the Holy Spirit of promise, which the Father sheds forth upon all those who are just and true.
They are they who are the church of the Firstborn.
These are they who have come to an innumerable company of angels, to the general assembly and church of Enoch, and of the Firstborn. - D&C 76:51-54 & 67

Q. What are we to understand by sealing the one hundred and forty-four thousand, out of all the tribes of Israel--twelve thousand out of every tribe?
A. We are to understand that those who are sealed are high priests, ordained unto the holy order of God, to administer the everlasting gospel; for they are they who are ordained out of every nation, kindred, tongue, and people, by the angels to whom is given power over the nations of the earth, to bring as many as will come to the church of the Firstborn. - D&C 77:11

This brings up a question regarding the 144,000. I mean the first group which have their C&E made sure, and help millions of others do so before the worst part of the millennial preparation. Is it possible to determine when the first of these 144,000 was ordained? It is merely a point of curiosity, as I suspect the first one was in the late 80's, but have no more than suspicion to back it up.

In addition, how quickly are people being added to this effort? If you started in 1988 and added 10 people every day, there would not be 144,000 until 2027. Please forgive my numerology, it was just on my mind.

And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bondman, and every free man, hid themselves in the dens and in the rocks of the mountains; 16 And said to the mountains and rocks, Fall on us, and hide us from the face of him that sitteth on the throne, and from the wrath of the Lamb: 17 For the great day of his wrath is come; and who shall be able to stand?

And I saw another angel ascending from the east, having the seal of the living God: and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea, 3 Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads. 4 And I heard the number of them which were sealed: and there were sealed an hundred and forty and four thousand of all the tribes of the children of Israel.
9 After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;

Q. What are we to understand by the angel ascending from the east, Revelation 7th chapter and 2nd verse?
A. We are to understand that the angel ascending from the east is he to whom is given the seal of the living God over the twelve tribes of Israel; wherefore, he crieth unto the four angels having the everlasting gospel, saying: Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their c foreheads. And, if you will receive it, this is Elias which was to come to gather together the tribes of Israel and restore all things.
11 Q. What are we to understand by sealing the one hundred and forty-four thousand, out of all the tribes of Israel--twelve thousand out of every tribe?
A. We are to understand that those who are sealed are high priests, ordained unto the holy order of God, to administer the everlasting gospel; for they are they who are ordained out of every nation, kindred, tongue, and people, by the angels to whom is given power over the nations of the earth, to bring as many as will come to the church of the Firstborn.

Is it possible for members of the 144,000 to have been born earlier in history and had their mortal lives extended - like the Three Nephites, or other translated beings - in order to be around to fulfill their calling today?

...Because the calling of the 144,000 so closely coincides witht he desires of those who wished to tarry, it also seems likely to me that they will be among the 144,000.

...I will say that instead of getting "burning in the bosom" experiences that instead I am getting flashes of insight that just seem to "feel right" and "fits more pieces in the puzzle" of my understanding.

Is it speculation that the leader need to be a certain age or are you looking at logic? I do not find it difficult to accept that this "leader" may even be a child.

I have never seen angelic manifestations. On the other hand, I have been receiving what I term as "pure knowledge" when I am busy doing something else.

I was reading a book a few months ago. I can remember the words that I was reading. I then remember that my mind was filled to capacity with the absolute knowledge that a certain world event that had occurred was not how I had originally learned. I knew perfectly the individuals that were responsible for the event and I knew why. It was interesting that the book I was reading had been published in 1971 and that this event occurred many years later.

After I put the book down, I was sure that it was something I had read because I could remember exact phrases and what led up to the event. I picked up the book but the words were not there. Only then, I understood that this was pure knowledge only as the Holy Ghost can teach. This has happened several times before and since but this particular event was something I wasn't even wondering about.