(C71) [U.R.C (Momoya Show-Neko)] Seisai Ranbu | Xing Cai Ranbu (Dynasty Warriors) [English] {Doujin-Moe.us}

That is only an over simplified version, of course, basing off the common joke about a strong, healthy man accidentally drinking 'Yang-rejuvenant' medicine... which is often aphrosidiacs mixed with some stamina (lungs, heart, muscle) -enhancing medicines. A common comedy trope, and an also common way for authors to deal with unresolved sexual tensions.

What they say when saying... rejuvenating the Elder. Well, in Chinese Medicine, the Humours are simplified into Yin (feminity, lethargic, weakness, bored of sex, etc.) and Yang (masculinity, energy, strength, overflowing desire for sex, etc.), and of which diseases are caused by improper balance of those. Old people usually lacks Yang, so in order to rejuvenate them they eat and drink Yang-positive stuffs... in this case the rejuvenant potion aka mana potion in game. This also means that the 'mana' potion has... an aphrosidiac effect, as seen here.

What the Fuck!