If the Big Bang occurred 13.8 billion years ago, then take this value of how old we all are since reincarnation doesn't work in a linear way. You'll experience one if your future selves after this one or go back 4,000 years or elsewhere in another realm for that matter.
BB is expanding into our future; it didn't mean a conventional explosion of matter into existing space. Instead, it was the rapid expansion of space itself.
Now you can see how the big picture works if you bring together the concepts of singularity, BB, yin-yang, the five dimensions of yy, reincarnation, sentient beings being eternal and the Tao itself (sum of all consciousness).
I firmly believe the historic Buddha experienced the BB. Other seekers may or may have not experienced it directly.