Ooya-san wa Shishunki! (Landlord is in Puberty!)
The four-panel manga follows a protagonist who is living alone for the first time after finding employment. At his tiny, no-bath apartment he finds a landlord who looks like a little sister. She does the cooking and housework, so sometimes seems like a grandmother, but she also enjoys a normal middle school life with her friends.
[Source: Anime News Network]