When Our Lord Jesus Christ said to the Jєωs that they had to eat His flesh and drink His blood so as to gain eternal life, do you think that they did not find it ridiculous? And nevertheless it was the truth...
What do you find "ridiculous"? The old age? Jeanne Calment and several other people reached this age...
In my opinion, the only thing that may be hard to believe in some way is the fact that the Freemasons were not able to kill Paul VI when he was still captive in the Vatican. However several private prophecies described this miraculous protection; and the reason of this protection is that if Paul VI had died, the Apostolic succession would have been interrupted (which is not possible).
Paul VI's survival is a dogmatic fact since he is the last pope peacefully and universally accepted by the whole Church. If he were dead, a legitimate pope would have been elected long ago. It is simple, very simple indeed.
Given the ignorance and blindness of our time, I could give many more arguments, you would still not believe me.
However, if you think that "Amakusa and some Frenchies are the only fools who believe in it", you should have a look on this recent American website, which is based on a much different material than mine:
https://pontifexverus.wordpress.com/The information of this website is not in full accordance with the Swiss exorcisms, and its sources have not all the same degree of reliability: in my opinion the most reliable source is Father Zorza, and it is clearly said that the latter was informed of Paul VI's survival by the assistant of a highly placed Cardinal.
I insist on the fact that the administrator of Pontifex Verus is not an "Amakusa bis". He has not re-used my own material, and he does not give the same arguments at all. I did not know this man before he created his blog.
Paul VI's survival is a much more serious subject than you can think, and it is much more grounded that the fairy tale of the "Siri thesis". I personnally know a French priest, who lives one hour from my home, and who has seen Pope Paul VI alive in Fatima in 2007; he has even talked to him. He was in the modernist Church and he was persecuted by some priests and bishops; he was forced to leave his parish (following a meeting with his bishop), and exactly one year later he received a letter where he read that someone offered him a pilgrimage to Fatima; he went to Fatima and after he had bought a statue in a shop, he met the Holy Father, who had the black cassock (so as to remain hidden). Paul VI ordered him to celebrate the tridentine Mass, and it is the way this abbot was converted to the true faith.
In France, several persons have been revealed by God that Pope Paul VI is still alive, including two of my own friends.
On the contrary, I have never met a sedevacantist who was revealed the "truth" of sedevacantism.