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?