After the Rain is a Winter 2018 anime about a 17-year-old girl named Akira Tachibana who has a massive crush on her 45-year-old manager, Masami Kondo. The premise may sound sketchy to some, but it's not a story about an older man taking advantage of a young girl. Rather, it's a story about how Akira's love for her manager helps her regain her love for track, something she put aside after sustaining an injury - and how her attention reminds Kondo that before he got married, had a child, and got an uninspiring job, he wanted to be a writer. After the Rain takes a difficult subject and turns it into something beautiful - but are there other anime like After the Rain? There are plenty!
Which one you should watch depends on what it is that attracted you to After the Rain in the first place. If you're looking for another story about age gaps, you may want to check out The Garden of Words or Ristorante Paradiso. If you want something that focuses on the funny parts of working in customer service, Blend S and Working!! might be up your alley. Want to see a story about regaining your passion for a lost art - specifically running? Try Run with the Wind.
No matter what you're looking for, there's an anime similar to After the Rain that's perfect for you.