Hi , Gotama realised that with birth as condition , aging and death comes to be but how did Gotama as an unawakened bodhisatta came to realise existence (assuming it is past live) ?
SN12.65
At Savatthī. “Bhikkhus, before my enlightenment, while I was still a bodhisatta, not yet fully enlightened, it occurred to me: ‘Alas, this world has fallen into trouble, in that it is born, ages, and dies, it passes away and is reborn, yet it does not understand the escape from this suffering headed by aging-and-death. When now will an escape be discerned from this suffering headed by aging-and-death?’
“Then, bhikkhus, it occurred to me: ‘When what exists does aging-and-death come to be? By what is aging-and-death conditioned? ’ Then, bhikkhus, through careful attention, there took place in me a breakthrough by wisdom: ‘When there is birth, aging-and-death comes to be; aging-and-death has birth as its condition.’
Then it occurred to me: ‘When what exists is there rebirth? … continued existence …