This TV series followed what's now a very common chain of events. It started as a light novel series, then became a Manga series, and is now serialized as an Anime TV series. The series is 12 episodes of about 22 minutes each.
Our main character is Ryoma Takebayashi (voiced by Emily Neves and Chris Rager in the English version). We learn in the first episode that he's 11 years old, having been living alone in the forest for three years taming slimes (and practicing magic and some martial arts). He's shortly taken in by a duke's family. And we find out that he was originally a 37 year old Earthling who died of Karoshi (death-by-overwork ... a common enough Japanese malady) and was brought to the world of Seilfall by three gods who liked him - and wanted to borrow some of Earth's magic.
The series is unrelentingly sweet and upbeat. We never see bad people (the closest we ever come is a mention that someone's been embezzling), everyone is lovely. There are many dangerous creatures, but Ryoma is incredibly talented and can take care of pretty much anything. The series is full of life lessons about being nice to strangers, having faith in people, and treating your employees right.
It's a bit creepy that this 37-year-old-in-an-11-year-old body is clearly headed toward a romance with an actually-11-year-old girl (Eliaria Jamil, daughter of the duke's family). The gods explaining to him that he's going to experience "infantile regression" (that's how it was translated into English) - but as he's clearly maintained his old memories and lots of skills from his previous life, this is less than convincing.
According to Wikipedia: "A light novel ... is a style of young adult novel primarily targeting high school and middle school students." I guess this series would make sense for people in that implicit age group - from 11-15? Although I think this would be too squeaky clean for the expectations of North American 14 and 15 year olds, who would probably want at least a little more darkness?