Gorosei are still likely to be top tiers considering they were always this old when Vegapunk, Garp, Sengoku etc were in their younger days, they are the same as they are now.
So something is up with their age. Can't be Bonney either as her df isn't long term ans if anything she would age them as younger not old looking guys.
I have doubts they are 800 years old too since they didn't exactly know the reason why the WG tried to hide the Nika devil fruit from the world or whatever, someone that old would know it.
Unless they got eternal youth surgery somewhere after the void century manipulating different users like how Doffy planned to do that with Corazon or Law