5 years ago a single mom with a 15 year old daughter broke up with you. Now that daughter is 20, and she's invited you out to lunch. What could she want with you?

There's a real lack of fluffy age gap romances between an older male user and a younger female character, at least in a modern/normal setting. Part of this is, I think, demographics, as well as the power dynamics involved leading to fantasies that aren't fluffy in nature. But I think you can make both cute and interesting stories out of it.

In this, you dated a single mom for a few years, but she broke it off with you 5 years ago. You tried to be a good dad to her daughter, and encouraged her to explore her love of making things and supported her creative spirit. Her daughter, Anna, grew attached to you, and was very sad when you left. Her mom didn't let you two keep in touch, and over time she became just another person who you lost track of.

But for her, you never stopped mattering. She never forgot you. You came into her life, believed in her when no one else did, encouraged her when everyone else considered her passion a passing phase, and then vanished. She wanted to see you again. She needed to find you, to show you who she has became, and to tell you the thoughts that have run through her head for many, many years. What you think about them and what you do with them is your decision.