Who did Kaido fight to get stronger over 20 years, Queen's fat ass? The whole point of the Middle Generation is that fighting subsided due to the new balance. The Shichibukai rose. Yonko were established and entered a stalemate long ago. BM/Kaido hadn't seen each other in decades. Neither had Shanks/Whitebeard. Shanks/Mihawk hadn't fought for at least 12-13 years.
Your 30s is like 90% of your prime. Shanks is still in his 30s. Roger/Garp took down Rox in their 30s. Even if Kaido got stronger, it wasn't by a whole lot.
current Garp is 78 . and Rocks battle happened 38 years ago so Garp was 40 years old .... Roger though was 39
But yea as of now there is nothing solid for me to assume Kaido grew a lot stronger .
• the argument that Kaido was matched by Moria , so Kaido must be a lot stronger now
> it could be that Moria was just that strong . the dude also gotten weaker as Doflamingo , Jinbei implied .
and his motto when introduced in Thriller Bark was "rely on others"
he got lazy , fat , lost his chin , and relied on Zombies to take a revenge on Kaido .
Moria's regress of power level is the most severe in this series , he regressed a lot more than Rayleigh
Kaido on the other hand was never hinted to be weaker .... infact he could stay as strong as he was when fighting Oden until now .
• the argument that Kaido must have grown a lot stronger in these 20 years because WB went from getting defeated with BM Kaido Xebec just by Roger and Garp , to being Roger's equal in like , 10 years
> except we don't know when WB got his Gura Gura DF , which is a colossal boost to his power level . did he had Gura2 when defeated by Roger and Garp ? we don't know that
meanwhile Kaido when fighting Oden already had his Dragon Mythical Zoan DF for 5 years at least , see chapter 969
• the argument that Kaido was hesitant in taking on Oden and Wano's chivalrous forces 5 years prior to this ( Kaido fighting Oden ) , while Kaido 2 years ago was seeking to kill Whitebeard who had his crew , and 43 Allied Captains
> yet Kaido didn't mention how he got stronger . or Oda
and for wanting to kill Whitebeard part , Whitebeard also at that moment was taking on World Government's 2 greatest forces
( Marine Headquarters and Warlords )
so that was indeed a perfect moment to take out Whitebeard .
when Whitebeard and his crew and 43 Allies weren't taking on Marine Headquarters and Shichibukai , from what we know Kaido never tried to kill him
the argument that could be legit to support Kaido being stronger is , that he challenged other Emperors and Navy 18 times ....
but even then i'm still not convinced for now .... if he was just getting destroyed in those challenges ( because he was alone ) then i'm not sure if he grew stronger
Anyway Oda could've easily pointed out Kaido grew stronger in these 2 years in a narrator box , but he never did that
oh yea , the argument that Kaido grew stronger because he is called WSC now . i think this could be because he has the most Feats out of all top tiers ( challenged other Emperors and Navy alone , endured over a thousand tortures , sunk 9 different prison vessels )
so i can understand if he gets rumoured as being the strongest top tier ( i do believe he is stronger than other 10 top tiers but by tiny margin )
at last , maybe Kaido grew stronger , but a lot stronger i'm not sure .