Not yet. You can quickly add page numbers to your document in Word Online, and you can hide the number on the first page, but to start page numbering later in your document, open the document in the desktop version of Word.
Then, follow the instructions in Start page numbering later in your document. (For Word for Mac, see Start page numbering later in your document in Word 2016 for Mac.)
When you’re done and you've saved the document, you’ll see the changes when you reopen it in Word Online.
Tip: Word Online works seamlessly with Word and other Office desktop programs, and we update it based on input like yours. For the latest feature announcements, visit the Office Online blog.