These are my immediate impressions from these questions.
1.) At what age do our beliefs begin having an affect on the Afterlife experience, or does age even matter?
If reincarnation is true I would logically assume that our beliefs affect our afterlife experience before we are even born, in our previous lifetimes, in some way or another, no matter what happens during this time around. This time around, age would be irrelevant. I would assume that all personal experience would be relevant.
2.) Is there a certain point at which a person has gathered enough beliefs as to have an affect on their Afterlife experience or do any and all beliefs have an affect on the Afterlife experience regardless of age or level of innocence/rational cognition?
Following the logic of this site I would assume that our beliefs cannot help but affect how we see the afterlife no matter why we have them and that we are influenced for better or for worse by those who greet us or by the personal experiences we have after crossing over.
3.) Do fleeting beliefs have an affect on the Afterlife experience, or opposingly, do beliefs have to be deeply engrained to have an affect on the Afterlife experience?
I would assume that fleeting beliefs might be present in the afterlife also, and all would affect experience there, as our beliefs, no matter of what duration, are connected to experiences which have meaning for us.
4.) What if I were to say (and think), "This is what I believe"... but, at the same time it wasn't something that truly and sincerely resonated with me?
Then your uncertainty would cause you to be more easily influenced for better or worse by those who greet you in the afterlife.
5.) Beings the ego is not that which merges with the light, but rather is part of this physical embodiment... Are beliefs solely part of the transitioning/separation process (residual of our Earthly life), henceforth stronger during the initial transition into the Afterlife and fainter as the transition progresses into the various deeper states of the experience?
I would assume that individual beliefs and individual experience are possibly maintained in some way, preserved in a private or public fashion, for revisiting or renewal of an individual frame of reference. However, I suspect that deeper experience beyond the "pleasures" of heaven or the prospect of immediate reincarnation would be much broader, and impossible for us to comprehend with a human mind in its subjective frame of reference.
Well, that all sounds very dry and unappetizing the way I have stated it...so, believe as you like! It does seem like there's lots of love to go around there...best to look for the light wherever you find it.
love, blink