GREP Styles puzzle: apply character style to the first half of every word

You can do it e.g. with the script below, for all stories in the active document. The script gives the character style 'bold', so you have to define it beforehand.

var doc = app.activeDocument;
for (var s = 0; s < doc.stories.length; s++){
	for (var w = 0; w < doc.stories[s].words.length; w++){
		for (var c = 0; c < Math.ceil(doc.stories[s].words[w].length/2); c++){
			doc.stories[s].words[w].characters[c].appliedCharacterStyle = 'bold';
			}
		}
	}

Alternatively, for selected text frames, not including overflow text:

var selTextFrames = app.selection;
for (var t = 0; t < selTextFrames.length; t++){
	for (var w = selTextFrames[t].words.length-1; w >=0 ; w--){
		if (selTextFrames[t].words[w].isValid){
			for (var c = 0; c < Math.ceil(selTextFrames[t].words[w].length/2); c++){
				selTextFrames[t].words[w].characters[c].appliedCharacterStyle = 'bold';
				}
			}
		}
	}

I'm not an expert in GREP - but I think you would need to search for each length separately.

Something like this:

1st step to "split" words - where "{2}" determines number of letters in each "half":

Then style upto %:

Then just remove "%" styled Bold.

But I'm sure someone will be able to do it in one or max two steps 😉

Or it could be easily scripted.