Is your feature request related to a problem? Please describe.
There's no way to stop (or start) the aging process of graves. This could be a problem for people who want to use them in different stages for decoration.

Describe the feature you would like to see.
Similar to copper, using a honeycomb item on a grave should stop it from aging -- and to start it back up again you should need to simply right click it with an axe a shovel (more fitting).

Commit 334777d implements the prototype for this feature. I'm going to close this for now, but I do plan on tweaking the functionality in the future:

The way this works right now is that every GraveBlockEntity has an noAge attribute attached to it (NBT). If the value is 1 then tickDegradation will skip over the block; otherwise it will try and age.

But, if you look at Minecraft itself as an example, there are Waxed variants of each Block of Copper.. I'd like to do the same, because this will completely remove the block from the degradation cycle and reduce processing on the block(s) slightly.