Is it normal that my ex-step granddaughter and i are in a relationship

I'm a 58-year woman. She's 23. We've seen each other for many months. She asked if she could move in with me and I let her. She loves me and I'm so flattered with her and it's remarkable how we fit each other. People think that we are mother and daughter until we show affection the way we do. She says that she wants to be with me forever. I just don't know if she'll still want me even 10 years from now, but I'll enjoy it for however long it lasts.