People keep assuming that the Regen is tied to the Gorosei not aging. I believe the Gorosei not aging is because of Law's Fruit.
If this is Imu's power, and Imu is as old as Imu seems to be, it makes no sense to assume that in the last few years Imu figured out how to do this, rather than Imu knowing how to apply these powers for a very long time.
So, yes, Garling should have had Regen on God Valley, and Newgate very may well have been scarred after Garling regenerated from a blow and surprised him.
Once Law's Fruit was lost to the WG, they could no longer make new Gorosei that lived forever.
So, Garling, while having the same Regen, will probably still age. I assume Garling WILL get some Yokai form from Imu, though.