Cosmicsearcher142,
Looks like I am not the only one with all these questions!
First, your question was expressed by the 17th Century physicist Blaise Pascal in the following way:
“When I consider the short duration of my life, swallowed up in the eternity before and after, the little space which I fill, and even can see, engulfed in the infinite immensity of spaces of which I am ignorant, and which know me not, I am frightened, and am astonished at being here rather than there; for there is no reason why here rather than there, why now rather than then. Who has put me here? By whose order and direction have this place and time been allotted to me?”
In my own search to these kinds of questions, I came to the conclusion that time is essentially mental, even though it has some physical element in it (otherwise you won't see it in so many physics equations) . The flow of time can be just an illusion. For example, in his book "About Time", another physicist (a contemporary one) Paul Davis imagines taking the sequence of one's lifetime, and having the time pointer go in random order instead of linearly forward, the person will still perceive time going forward linearly. So, instead of 2:01pm follows 2:00pm, and 2:00 pm follows 1:59pm, let's have time flowing in the following order: 5pm, then 3pm, followed by yesterday's 5:30pm, and so on and so forth... totally out of sequence. If there is a being who is outside of time, this being will be able to perceive the sequence being out of order. But for a being inside time, this "out-of-order-ness" simply is hidden. Just like if you play a DVD in random order, sudden forward, sudden backward, you can see the disorderness because you are outside of the DVD time. But for a character inside the movie, this randomness is completely hidden because as far as he is concern, when a certain frame is up, he would be doing a certain thing. When another frame is up, he would be thinking about another thought, perhaps anticipating his future. The order of the frames being played affects the viewer, but not the character inside the movie. The question is what determines which frame is being play at this moment in this cosmic movie we are in? And what determines why is now playing the frames that have "you" in it?
We are all characters inside a cosmic movie, and so the time is necessary linear for us.
As why you are only born now, and not a hundred years ago, despite the probability of being born any time within the last 10 mellenia before Jesus was much greater than being born on the day you were born given the range? That is a great question. But the question assumes that you are your current body. In fact, a generalize question to the question you are asking is the following: Why is your consciousness associated with the physical body you call your own, while there are billions of conscious bodies in the universe that your consciousness could have associated with, including those in the past and those in the future? Why were you born you? Why when a physical body was forming in a certain womb, you started to gain "consciousness"? What linked you, the consciousness, to the physical body? In the philosophy of mind, this question is closely related to the so-called "The Hard Problem": Assuming materialism is true, how does materials moving around (all physical systems are materials moving around, including the human bodies) create a "first person view"? Is there a possibility of having a physical system (read body) that is an atom-for-atom replicate of your body, which behave exactly like you (the law of physics dictates that it behaves like you since it has the exact same DNA and memories you have), but is actually unconscious? Something that is totally "dark" inside? This possibility is the existence of the so-called "phenomenal zombies" or "philosopher's zombies", or simply p-zombies.
I have written an ebook title "Where are the zombies?" about it. If you are interested, you can google the title with a qualifier "ebook" and you will find it. There are free versions around. The late version was updated in Oct. of 2011. Maybe you will enjoy reading it.