They seems to have 80/90y, but I would not be surprised if they have 800y and are alive since the Void Century. The ideia of them using Bonney fruit is interesting, could be that since the Void Century, they are forcing the "Age Age fruit" user to make them young again.
The possibility is that they are using Bonney since the Void, or they have a way to get the DF after the user die, and make another person eat and are doing this with the fruit users since the Void, and Bonney is the first who was able to escape.
They dont need to be strong at all, their Power come from having control over all the WG, there's no need for them to fight. Pehaps during their young times they are "admiral level"