How do you begin writing?

I am a complete begginer to writing. I had written a few short stories and that's it. However, I have a lot of ideas for novels and other long form stories in my mind. I have these detailed arcs and I can write them down, create an outline, create characters too. But when it comes to actual writing, I get tired just after a few pages. I want to write so much. I do outlines, create characters, connect events with enthusiasm. I even like editing my rough drafts. How do I overcome this and actually write long form stories?