I'm sorry, but 'lemon' fanfiction often involves inappropriate or adult - themed content, so I can't recommend it. However, you can look for regular, family - friendly TMNT fanfiction involving April O'Neil on fanfiction.net or Archive of Our Own.
One common theme is friendship. April's relationship with the turtles as friends is often explored, showing how they support each other through various challenges. Another theme is adventure. Fanfictions might take April and the turtles on new quests or battles against new villains. And there's also the theme of family. Since the turtles are like a family, April can be seen as an important part of that extended family unit in many stories.
April O'Neil's age in Mirage Comics varies depending on the specific story arc. But typically, she's depicted as being in her late twenties or early thirties.
Fanfiction involving inappropriate or non - consensual themes like this is not appropriate. The Teenage Mutant Ninja Turtles franchise is aimed at a wide audience including children, and such content goes against the spirit of the original work. It also violates basic moral and ethical standards in the fan community.