A ghost's Horrifying Visage can age a creature as follows:
Horrifying Visage: Each non-undead creature within 60 feet of the ghost that can see it must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d4 x 10 years. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this ghost's Horrifying Visage for the next 24 hours. The aging effect can be reversed with a greater restoration spell, but only within 24 hours of it occurring.
What's unclear is whether this can be fatal or if the effects are purely cosmetic. For elves, this is likely not an issue, but does a human simply go from a healthy young adult, to an elder who likely works out very regularly because there is no stat adjustments for age (that I know of)?