Enter the search term in Global Search (Ctrl+K), then in the results tab you'll see a histogram showing the number of results per year. Click the bar for a year to see a breakdown by month, then click a month to see a breakdown by week, ... You can also hover on the Filters on the left to see results highlighted on the bars.

I forget how, but I've actually turned OFF that histogram. Hate it. Meant having to search, essentially, TWICE to simply get a list of emails meeting my criteria.

I thought I might be able to enter something like, "Age:365-9999" to get anything older than a year, etc. Some kind of advanced search "lingo," as I'm used to in other places.

To search a folder for messages that fall in a specific date range, try the Search Messages option from the folder right-click menu (see picture).

Sorry. I know you're trying to help. But I want to search all folders, all accounts. Not one folder at a time (I have many) in a single account (I have many). If TBird can search for text, I'm not sure why it can't search for/by dates!

You might be able to apply date and time search criteria to all folders by using the Expression Search / GMailUI add-on.