I believe that the Gorosei have attain immortality through The Ope Ope no Mi. I was just thinking about this and if they are immortals defeating them is going to be a challenge.
I also believe this theory U_UI believe the WG used bonney's powers to make them younger because Akainu came to personally retrieve her. So they're not really immortal but I would like a second youth for those guys.
I don't want a potential final fight of one piece against 5 near death men.