@Roarofwaterfalls There's a common misunderstanding with this potion, a lot players expect it to actually change your sim's age back to the previous age, like young adult back to teen, but like
@crinrict said, how it actually works is just resetting the current "age bar" so that it will be longer before your sim ages up. They basically just get some days "refunded" to their lifespan. If that's the issue, that you thought they'd be going back to a younger age group, you're not alone there. The name of the potion does kind of make that an easy misconception.