Potion of Longevity

From Dungeon Master's Guide, page 188. Found on Magic Item Table D.

Description
''Potion, very rare. 0.5 lbs.''

When you drink this potion, your physical age is reduced by 1d6+6 years, to a minimum of 13 years. Each time you subsequently drink a Potion of Longevity, there is 10 percent cumulative chance that you instead age by 1d6+6 years. Suspended in this amber liquid are a scorpion's tail, an adder's fang, a dead spider, and a tiny heart that, against all reason, is still beating. These ingredients vanish when the potion is opened.