If it comes down to having to do this in a game, I basically use a conversion of the old Potion of Longevity.
This must be researched and is a very powerful potion.
Potion of Longevity (Minor)
This potion reduces the character's age by 1d12 years, restoring youth and vigor. The entire potion must be consumed to achieve the desired results. Each time one drinks a Potion of Longevity the imbiber must make a Fortitude saving throw (DC 5, +1 for each previous application of a Potion of Longevity). A failed saving throw results in the effect reversing all previous aging reductions, bringing the character suddenly to their normal physical age.
Caster Level: 4th; Prerequisites: Brew Potion, slow, lesser restoration; Market Price: 900gp
Potion of Longevity (Intermediate)
This potion reduces the character's age by 3d12 years, restoring youth and vigor. The entire potion must be consumed to achieve the desired results. Each time one drinks a Potion of Longevity the imbiber must make a Fortitude saving throw (DC 5, +1 for each previous application of a Potion of Longevity). A failed saving throw results in the effect reversing all previous aging reductions, bringing the character suddenly to their normal physical age.
Caster Level: 8th; Prerequisites: Brew Potion, slow, restoration; Market Price: 2,700gp
Potion of Longevity (Major)
This potion reduces the character's age by 6d12 years, restoring youth and vigor. The entire potion must be consumed to achieve the desired results. Each time one drinks a Potion of Longevity the imbiber must make a Fortitude saving throw (DC 5, +1 for each previous application of a Potion of Longevity). A failed saving throw results in the effect reversing all previous aging reductions, bringing the character suddenly to their normal physical age.
Caster Level: 14th; Prerequisites: Brew Potion, slow, greater restoration; Market Price: 7,100gp
Potion of Longevity (Master)
This potion reduces the character's age by 10d12 years, restoring youth and vigor. The entire potion must be consumed to achieve the desired results. Each time one drinks a Potion of Longevity the imbiber must make a Fortitude saving throw (DC 5, +1 for each previous application of a Potion of Longevity). A failed saving throw results in the effect reversing all previous aging reductions, bringing the character suddenly to their normal physical age.
Caster Level: 18th; Prerequisites: Brew Potion, time stop, greater restoration; Market Price: 21,300gp
When you throw Wish into the mix, I allow it to create the Potion of Longevity (Major), as it can create any item of up to 15,000gp value.
Sweet and Simple.