Jinbei = 46 years old now. Meaning he's essentially at his peak or near it.
There are few old characters in One Piece, that are getting stronger despite their high age, but there are few factors involving them:
Capone Bege, Urouge, Fujitora.
Capone & Urouge really started their journies on the seas about 3 years ago. In addition to that, they have Devil Fruits, which allows them to grow even if they were to decline physically. Compared to them Jinbei has been on the seas for years and has been wanting to protect Fishman Island, which is why he's been jumping into Yonko crews + being a Warlord. So you can bet your ass, he's been training his ass off for the last decade+ .
With Fujitora he was already a world renowned monster, but at the age of 50+ attained a Devil Fruit, that adds on to his power, that allows him to get stronger than he was before, despite declining physically.
Jinbei neither has a Devil Fruit and neither has he just started his journey or training to peak out.
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Franky should surpass Jinbei if he's gonna surpass Kuma, who's being called invincible by the CDs.
Usopp should also surpass Jinbei if he's gonna surpass Yasopp who's meant to be "Yc3" for Shanks, but if Yasopp isn't YC3, then it doesn't matter.