The Google Gmail search box is powerful in helping to find past emails and information quickly from your repository of current and archived emails. There is logic within the search box which you can use to further define your searches. One is searching on a date range. You can do this by using the syntaxes:
before:YYYY/MM/DD
Both lines can be used in a single search query string to designate a range of emails.
From there, you can check all of the emails to apply a certain action such as: Delete, Archive, Mark As Read, etc.