Chronofage

This spell is usually cast as a ritual but at DM discretion it can be cast within combat (10 rounds concentration to cast).

You touch a target creature. The Target permanently ages up to 50% of his current age and you rejuvenate half of that amount. If the target succeed a constitution saving throw, it will only affect as half of the intended. Example: if the target is a 50 years old human, it will age 25 years on a failed save and you will rejuvenate 12,5 years. On a successful save, it would age 12.5 age and you rejuvenate 6 years and 3 months.

If the target is a creature that has very long lifespam (elf, dwarf, dragon for example) and you do not have a very long lifespam (human, halfling, orc...), you cannot rejuvanate to an age inferior to 10 years old. Example: if the target is a 500 years old elf, it will age 250 years on a failed save and you should rejuvenate 125 years. If that is not possible, you will rejuvenate to 10 years old. 

You lose any effect regarding age your character has. You retain all your current powers and memory. The target, on the other hand, suffer all the problems of aging. If it goes beyond its maximum lifespam, it will die of old age a number of days equal ot its constitution modifier. Both you and the target suffer one exhaustion level at the end of the spell.

This spell cannot target undead, constructs or creatures that dont age. If the target is under a spell that prevents aging, this spell will automatic fail.

The resulting age is considered natural and permanent and cannot be restored with Greater Restoration or similar spells.