On Twitter, Google’s John Mueller and Google’s Danny Sullivan said that you don’t have to worry about the date that is displayed next to the cached version of your web page:
The cached page is not always representative of crawling & indexing, so I generally wouldn't use the date shown there as a sign of a problem.— ? John ? (@JohnMu) May 13, 2019
Yes, I'll pass this on. But please keep in mind that the cache date does not reflect the current date of a document indexed in our systems.— Danny Sullivan (@dannysullivan) May 10, 2019
The cache is not related to indexing and the cached version isn’t necessarily the version that Google has in its index.
If your website has ranking problems, it is very likely that this is not caused by indexing problems of Google. It is much more likely that your website either blocks Google’s crawler (wich you can fix by checking your website with the website audit tool), or that your website hasn’t been optimized yet (which you can fix with the Top 10 Optimizer tool).