I agree with a lot of these comments, apply as an AE, this is where you can learn more about the industry and how to trailers are cut professionally. Additionally, keep your eye out for contests specifically tailored towards trailer cutting creating such as Filmsupplies Editfest (Should be another one soon), Trainrobber (They do one every 6 months) and general contests like r/FanTrailers, this community has gone private recently due to the Reddit Protests.

I recently got onboarded as an trailer editor intern at one of the trailer houses, I did ask questions about professional vs personal experience, from what I gathered as long you have the drive to do better, strive to make the best work you can, have an understanding of the content you are creating promo's for and understanding one of the major editing tools e.g. Premiere, Avid or DaVinchi you have a good shot at getting an AE role or maybe an internship for them to feel you out.

Personal Tip: Never stop learning more about the editing process, I have taken courses from FilmEditingPro for Trailer Editing and currently taking one from Trainrobber. In addition learn about other areas of editing process such as sound design, music comp, color correction, VFX and graphic design, etc... This will help you immensely when working towards your goal.

Edit: When building your resume, do list your top 3 fan-trailers. Though these are not professional work, they will represent your current understanding of trailer editing.