Eternity Beam

You blast a 10 foot wide beam of pure astral energy in a straight line from your location that rapidly ages any creature it touches. Any creature that starts their turn in this area, or enters the area for the first time on its turn makes a Constitution saving throw. On a failure, the creature rolls 1d6 and temporarily ages that many years, taking necrotic damage equal to this roll. When a creature exits the beam, they revert back to their original age before they were within the beam. If a creature that has been aged by this spell in this way reaches their maximum age limit, their hit points drop to 0, and they regain 1 hit point once they are no longer in the beam.