Please take this as constructive criticism meant in good spirit, I hope it comes across that way.
My first reaction is it's a nice starting point. Presumably you will be adding more content over time? A suggestion would be to focus on one period at a time. You're trying to cover the whole of human history up to the twentieth century, that's probably too big a subject for one person to do comprehensively enough for it to be useful from an educational point of view. I'm assuming you've taken this approach because of a genuine interest in the whole of human history - good, but too much work for one person (it would be a full time job).
The "Significant People" heading only has two people in it at present. (Admittedly I'd never heard of Andreas Vesalius so I've learnt something new today!) Personally I wouldn't publish this page until you've got a few more biographies on it. It would be good as well if you linked the information in the biographies to more in depth articles elsewhere on the site. (This is what I mean about focussing on one area at a time - it would be great if George Washington's biography linked to articles on his early life, the revolutionary war, his political career, etc.)
I agree with the Cornishmumofone's suggestion about getting it working on a mobile site too. If you design it on a computer, use the browser's tools to see how it will look on a phone and tablet. (In Chrome press Ctrl+Shit+i to get "Developer Tools" up, you can then use the drop down menu at the top to select different mobile devices to preview it on - the default setting is "Responsive" but the menu has iPhone, iPad etc.)
I think some of the content would be better spread across several pages. In some cases it works - Medieval History GCSE has "The Normans in Brief" and "Edward's Death and the Claimants to the Throne" are of course linked together - but on 20th Century KS1/2 it leaps from "Life on the Titanic" to "Life in a WWI Trench". Only a few years in time but massively different subjects.
I think you have complicated things for yourself by having different target ages groups. It might be better to focus on getting plenty of content for one age group before branching out. If you prefer to tackle all age groups whilst focusing on a particular subject I would suggest trying to publish the articles for all groups at the same time. For instance in the 20th Century section you have five subjects for KS1/2, one for KS3 and none for GCSE.
I would change the landing page to a more general overview of the site - a featured article, latest updates, social media channels, that sort of thing. Move the autobiography to an "About Me" sort of page. The reason for this is that if someone stumbles across your site you want to instantly show them what the site is about, not who created it. Your "hook" is your content. (At least until you're a famous historian!)
I like the selection of images you've chosen. Some of them appear very pixelated though because presumably the source images are different sizes (eg on the "How the Romans Conquered Britain" page, the Boudica image is much sharper than the Claudius one next door).
Feel free to ignore the rest of my advice but please follow this bit: make sure you clearly label the sources for your images. The fact that they don't have this information makes it look like you've just swiped images from a Google search and used them without looking up copyright. I'm sure that's not the case but if it is, fix it before your site gets a following (unexpected letters from lawyers are never nice). I suggest Wikimedia for finding images you can use freely, but even then I would recommend listing Wikimedia as the source. And for your own images, put a copyright message next to them - it won't stop people stealing them of course, but people can't claim they weren't warned.
As it stands - it's the sort of site I'd direct people to if their homework was "find out some facts about Roman Britain" or something like that. But there's not enough detail for it to be someone's primary learning source. It's a good starting point for your project though and it's clear you have put a lot of time and care into it.
PS. There's a spelling mistake on this page "Who Ws Living In Scotland?" - not being a smartarse, just pointing it out. That's the only one I've seen so far by the way, which is a better record than the BBC site has these days. 