Onnatachi no Miyako(1993)

The three elderly sisters Yaeko, Hanae, and Tsubomi from Cattleya na Onna-tachi are back! Even in their old age, they still feel like maidens! The three dynamic sisters are enjoying their twilight years at the nursing home "Cattleya Garden." One after another, young women in distress come to them for help. Aiko, a cocky gal with a sassy tone, got into an argument with Yaeko and her sisters on the street. She is 20 years old and in debt for 2-million yen, stuck with a no-good boyfriend who doesn't work and only getting them into more debt. Aiko sets her eyes on Professor Shinonoi, another resident at the Cattleya Garden, and tries to seduce him for his fortune. The lecherous professor falls right into Aiko's trap...! It's okay for old people to fall in love! A stirring new idea for an aging society! This is an ambitious work that overturns the conventional tropes of shoujo manga!

(Source: Office Manga, translated)