Not able to upload featured image for PAGES or Categories (not posts)

Please help! Note: my tone in this is not snobby, I'm just trying to make my point clear as to what I am looking for for because I am not very web literate. Thank you in advance :) I love the full width header image area of this theme. I chose it because I want a big beautiful responsive slideshow on the home page and big beautiful responsive image featured on each Page, post, and category/archive page, specific to the content of that page,post,archive. I currently have my header image set to "Excluding homepage, Page/Post Featured Image" which indicates that my pages and posts should feature their own feature image, and will default to the uploaded headers ONLY when a featured image is not chosen or is not enable, right? The point to uploading a featured header/several featured header images is to replace the header image on a post or page when there is no featured image set and enabled on that page right? Well, it seems that I can't EVEN SET A featured image for any of my PAGES or CATEGORIES. (posts work beautifully, so no worry there). I don't want to have a bunch of pages or category archives on my site that all have the SAME image over and over again, nor do i want Pages and archive category pages that randomly generate a header image that has nothing to do with the topic of that page (i.e. I could have a page called "Meet Me" and a picture of a Bear in Alaska could show up as the header, when I really want to feature a photo of me. OR I could have a category archive in my menu titled Islands and have all my posts about island show up, but then a photo of a mountain that I've uploaded to my featured images might show up as the header. That would make no sense. And it also wouldn't make sense to have the same boring header show up over and over again for everything but my posts OR for me to disable the header because then the site would be super boring). I want to be able to set a featured image for PAGES and set a featured image for the CATEGORIES so i KNOW which image will show up as the header. On the page editor, there is no featured image upload box like there is in the post editor, however, in the Full Frame Options at the bottom under the single page/post image layout, there is an option for Default/Featured Image/Full Size/ Disable Image, and if that option is even present, that means there should be a way to upload a featured image to the page right?? (Also, I just submitted a question asking why the Archive Content Layout option is not available when I create a new page. If this feature worked then all I would need is the ability to choose a featured image for pages...then my page titled "Islands" could have a photo of an island, and all my posts aboutu islands would show up underneath.) THANK YOU!!!