Here are some of the F/m stories I've written. Oops - edited to add that I missed the 18+ bit. I'm not sure how old all of the teens are.
Home Made Wine - a teenage boy drinks home made wine with a new neighbour's son. His mother sends him to apologize, and he discovers that he is expected to submit to a spanking as part of the apology. - might be 18+
A Totally Original Superhero Story - This isn't a spanking parody the first Shazam! movie. No, it's a totally Original Story. Wink, wink. Think about the teenagers from that movie and spanking. - probably not 18+
The Bait And Switch - written for story contest, it's a story based around a F/m spanking. 18+
Todd's Fantasy Comes True - High school student Todd has frequent fantasies about giving spankings and being spanked. A holiday break results in his fantasy coming true, or maybe he had a weird trip. - probably 16 or 17.
Yearning For The Past - A teenager lives in one of those old Great Houses (think Downton Abbey style house) that is open to tourists. He dreams about being born decades earlier when he would have been caned. He is a part of the house that is off limits to tourists, bent over a desk in the old school room, dreaming about being caned, when a woman enters his life. - I think this is 18+
The Spanking Sorcerer - Based in a modern version of Pathfinder (1st edition), this story has several spankings, including F/m of a teenage boy. Technically he semi willing submits to most of them, but that is when he is acting as distraction for the rest of the team. Oh, and he spanks a few girls. Check the spanking codes for each chapter. - the character is currently 18+, but most of the spankings happened in the past.
The Morning Flight And The Man-Boy - a F/m domestic discipline story. 18+
An Early Christmas Present - a teenage boy gets an early Christmas present, leading him to try to blackmail an older girl who lives next door. The girl doesn't like what he tried, and F/m.
Glass Wall - Set in a version of GURPS Technomancer world, a teenage boy has the ability to cast magic, but only one type of magic. He uses that magic to see a wall and spy on a girl, resulting in F/m. - probably not 18+
The Genius - Think a teenage Shelton from the Big Bang Theory being spanked by girls in his study group. - probably not 18+
Ghost Town - a boy in his early teens has the freedom to explore a ghost town. He finds signs that there were spankings happening when the town was occupied. He tries to track down a girl who lived there, who is now a mother, and F/m. Not 18+
Unexpected Witness - The Governess - A teenage boy is taken to task by his governess, and there is an unexpected witness to the discipline. Not 18+
Spanking Your Monkey... - a teenage boy is spanking his monkey to spanking porn when his aunt walks in on him. He discovers that he only likes fantasy spankings. 18+
Reaching For A Memory - an actor needs to act as if he is being spanked, but he doesn't know how. 18+
Switch - A Regretted Gift - a teenage boy attempts to get a girl switched, but fails at that as F/m story develops. - probably not 18+
Summer With The Relatives - a teenage boy thinks that he wants to get a spanking, only to discover that he doesn't. 18+
Returning To The Family Reunion - Might be a bit consensual, but F/m. 18+
Souvenir (Version 1) and Souvenir (Version 2) - a young teen visiting London (England) and tries to look at girls wearing knickers in a school supply store catalog. His mother decides that he should be able to buy some of those catalogs. Misunderstandings happen, and the souvenir isn't a catalog of schoolgirls wearing knickers but a tested cane and strap. Each story starts more or less the same, but goes off in different directions. - not 18+
Getting The Shrooms - someone is out looking for magic mushrooms when he accidentally sees a woman collecting on a spanking bet with a guy. 18+
Moms Taking Charge - Part 2 - A teenager discovers the Moms Taking Charge club, resulting in him getting spankings. Well, actually he discovers it in Part 1, but that is mostly a F/f story with only a bit of F/m bits. 18+
Magic & The School Nurse - has the school nurse spanking a pair of high school students, one M, the other F. - probably not 18+
The Spanking Lady On Patrol - Part 1 - a very minor superhero (the Spanking Lady) spanks both male and female bottoms. - could be 18
Here's hoping you enjoy one of those... | 
