Yesterday a friend of mine and I were reading the new spells from dunamancy. And we had a discussion about this 9th spell called time ravage.

Casting Time: 1 action
Range: 90 feet
Components: V, S, M (an hourglass filled with diamond dust worth at least 5,000 gp, which the spell consumes)
Duration: Instantaneous

The description says: You target a creature you can see within range, putting its physical form through the devastation of rapid aging. The target must make a Constitution saving throw, taking 10d12 necrotic damage on a failed save, or half as much damage on a successful one. If the save fails, the target also ages to the point where it has only 30 days left before it dies of old age. In this aged state, the target has disadvantage on attack rolls, ability checks, and saving throws, and its walking speed is halved. Only the Wish spell or Greater Restoration cast with a 9th-level spell slot can end these effects and restore the target to its previous age. 

The damage its meh, but the most confusing part is where it says that if the target fails the save it will magically age during 30 days until he died from old age. My friend defend that can kill anything for only 5k of gold. But in my opinion has a lot of errors. First of all some creatures are inmune to magical age like lv 14th monks. But does dragons, undead, fiends and celestials can die for age even if its magical? I think no, we know for example Orcus and the demogorgon are the oldest demons and in hell the older you are the stronger you are. I don't think they can die so easy. My friend also try to convince me that they have disadvantage on everything if they fail. I literally get mad at that point because what he said has no sense, literally every big enemy from DC 16 to 30 has at least legendary resistance, in addition they also have Cons saving of +15 so basically they can pass the saving throw easily so you just spend 5k of gold on making 10d12 of damage and a little possibility to kill someone in 30 days and can only be saved using wish or greater restoration at 9th level.

I wanna hear your opinions about this and want to know who is more correct, my friend or I.

Legendary resistances run out and once they are gone a high level Chronu wizard has an auto-fail ability to defeat tje +15 Con.    It is called Convergent Future.

I would however rule that being immune to aging is possible.  I would NOT include Dragons in that as while they live for a very very long time, they clearly do age and die.

True dragons pass through four distinct stages of life, from lowly wyrmlings to ancient dragons, which can live for over a thousand years.

If you 'can' live for over a thousand years, that means that you can not live for 10,000 years.

The most obvious category of creatures that do not age are:

• Constructs
• Undead
• Fiends
• Celestials

Obviously these creatures do not age.

I could also see arguments that many Oozes and Elementals do not age. And finally, I can see individuals be immune to aging.

Thanks for your answer, I also think that constructs don't age, because they have the inmutable form ability which i think prevent them from aging. About dragons I dont really know if Tiamat or Bahamut can be affected.

Quote from IñigoLeon >>

Thanks for your answer, I also think that constructs don't age, because they have the inmutable form ability which i think prevent them from aging. About dragons I dont really know if Tiamat or Bahamut can be affected.

 
Tiamat and Bahamut are Gods so I'd say no.

Normal dragons do age and can die of it - just takes a really long time, but given the spell puts you right at the end of the lifespan no matter what, so they'll still be affected. Just know that casting it on the young dragon would instantly make it an ancient dragon and more powerful.

Any creature immune to being aged magically cannot be aged by this spell. Any creature that has an immortal lifespan suffers no effects of aging from this spell.

When in doubt if a creature ages or not, it is a DMs call.

Does the Tarrasque age?

Quote from IñigoLeon >>

Does the Tarrasque age?

 
No clear answer in 5th edition. It can lie dormant for centuries but nothing is mentioned beyond this. This would be a DM's call.

can only be saved using wish or greater restoration at 9th level.

As far as I'm concerned, any big baddie that you're fighting by the time you get level 9 spells probably has some way to access these spells long before the 30 day deadline. Certainly elder dragons shouldn't have a problem with it.