No idea. I don't think I've spent more than 60 hours on any particular character, and that's on Master where fights/dungeons take longer than normal.
Then you've certainly missed out on a lot of the fine detail, sights, and nuances of the game. Some rush through the world and just catch the obvious parts, others explore and see and do everything. I tend to the latter. My main char is at around 100 hours, and my stats show I've discovered 114 locations and cleared 54 dungeons- a drop in the bucket

I methodically explore each area I encounter, sneaking up every canyon till I can't climb no more, or get a 'You cannot go this way' message. Swim every river and lake and bay looking for hidden chests, delve into every canyon and hole, and peer out over the beautiful world from every awesome vista point along the way. My biggest problem, is that no matter which direction I choose to explore in, there are 3 other directions I'm neglecting!

I'm sure once I finally explore every bit of the whole world of Skyrim, future characters will not be spending so much time with the exploring part. But until that point, probably another 200 hours or so out... I'm lovin' it and takin' my time. I can't even fathom how people can rush through this game in less than 100 hours, and think they've actually come anywhere close to really experiencing it.