There is no set number of keywords per page. The reality is that the more keywords on a page, the less each keyword is used and the less likely it is to rank for a given keyword. It’s also important to note that the page with the most keywords isn’t always the best ranking page. Depending on the niche, pages with fewer keywords can rank better than pages with more keywords. The key is to balance the keywords on your page so that your page performs well, while not cluttering up the page so much that it’s hard for users to read and doesn’t perform well in the SERP’s.