In the Player's Handbook there are multiple spells that can bring a creature back to life. Resurrection, revivify (p272), and true resurrection (284) each have a clause that say that they don't work on a creature that died due to old age.
However, neither raise dead (270) nor reincarnate (271) list any such restriction. Does this mean that these two spells can restore life to creatures that have died of old age? In the case of raise dead what's the ultimate result?
As you rightly say, those spells contain no such restriction on bringing back a creature who has died of old age.
In the case of Raise Dead, the creature retains their original body and their original age. Therefore they are at risk of dying of old age again in the near future. The exact methods of determining how and when a creature dies of old age are up to the DM.
In the case of Reincarnate, the creature has a fresh body created for them which is "adult". They are not in danger of dying from old age again in the near future.
Of course it makes sense.
As soon as he is raised, he can be given a few potions of longevity so he will not die of old age in a near future.
It is very strange that a low level spell like Raise Dead is much better than Resurrection or True Resurrection, both of which has restrictions about it.
Probably the authors simply forgot to add the restriction to this one.
depending on your DM raise dead could be used to raise dead at specific ages, but it doesn't make sense to bring back someone who died of old age as they would more than likely be brought back in a way that they would die soonafter anyways.
