I think Kaido is around 62-63 years old
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He is definitely younger than Big Mom.
Kaido and Shanks are part of the new generation, while BM and WB are part of the older generation.
Being in the same generation DOES NOT MEAN they are in the same age
Example
Luffy is 20
Hawkins is in his 30s
Urouge and Capone are in their 40s
All are in same generation. But all have different ages. In fact, with WIDE GAP
So, Kaido and Shanks are in the same Generation in that they both SHINED as pirates around the same time. (EVEN THOUGH Kaido was big time pirate in Rocks 41 years ago, before Shanks was even born hahaha)
So, for that info, I think first, Databooks (which I believe the source of that info) Databooks are not entirely reliable, Shanks becoming a Yonko before meeting Luffy is an example of it being wrong info.
But also, EVEN if that info is true. I believe that it's simply meant that they both became officially recogized as Yonko around same period. Maybe 1-2 years difference.
But anyway. The fact that Kaido, was part of the Rocks 41 years ago. While Shanks is 39 years old now. And Kaido looked adult, not a child. It simply tells you that there is an age difference between them.
55 is the MINIMUM age I give Kaido.
62 - 63 is where he should be around, since we mostly believe he's younger than Big Mom who is 68
68 years old if Oda continued with the "Big Mom - Kaido" comparison as Oda makes them similar in a lot of things
Over 100 years some someone stated if Kaido's race played a role of him looking younger. Maybe his Dragon theme? or the Oni?
Remember that Giants can live 3 times as much as human, and someone looks youthful at his 100 years old.