To make your own Tumblr have an endless scrolling page (until you reach your very own first post), also known as autopager or autopage , you just need to paste a line of code into your description, but please, pay attention to the note after that.
Tumblr with Infinite Scrolling Pages.
Paste the following line of jscript code into your description box to make your blog endless scroll. It doesn’t matter if the description already has text or anything else, since this script won’t show up. Your description box is located in Customize »> Info.
NOTE: It is very important that, after you paste the code you retype all the quotation marks, there are a total of 4. Otherwise the endless scrolling page won’t work, and I found out this is the only reason many people complain that this code is useless when it’s not. Somehow the quotation marks get pasted in italics or backwards.