First it's better to stretch the AOC in a fantasy setting than a morden setting. People wouldn't mind a goblin having segs after two month than a 16 years old whom they can imagine.
Secondly, If you are trying to do H2H seegs, then it is better to keep both of their ages as close as possible. It would be even better if your mc is younger. Don't make the age gap too glaring.
Thirdly, make sure the reader understands what is normal in that world. Again it will work better in fantasy medieval settings than in medieval ones.
Last but not the least, clearly warn the readers in the synopsis. and include a trigger warning at the begining of the chapters with such content.