If the mark theory is correct then imo the Gorosei and the Holy Knights have different regeneration/immortality which is implied anyway
Think about it, Garling should’ve been immortal before he became a member of the Gorosei yet he’s clearly aged since God Valley
They’d still need a weakness that I’m unsure of
Gorosei and Imu got Perpetual Youth Surgery from Law's Fruit, before they lost it. IMO, one doctor realized the other doctors "working" on Imu and the Gorosei all died, and thought, "fuck it, I'm getting out of Mary
Dodge Geoise", and teleported his ass out of the Room
Gorosei and God's Knights gen Regen from the Abyss, and their Marks associated with it.
Gorosei have their own CoC/powers, they're strong on their own; it's the Perpetual Youth Surgery + Abyss Regen that makes them actual monsters
This is why Garling aged from God Valley to present day and Saturn didn't. Both have Abyss Regen, Saturn got Perpetual Youth Surgery around the Void Century. So, Garling will still age, unless they get Law's Fruit, making me think Garling will target Law.