Open Gmail
In the search bar, type older_than:1y to find emails older than 1 year
Change 1y to 6m, 2y, or any time period you want
Press Enter
Click the checkbox at the top to select all visible emails
Click Select all conversations that match this search if shown
Click the Delete icon
Open the Trash folder
Click Empty Trash now to permanently delete the emails
Repeat with other search filters if needed, such as older_than:30d, older_than:90d, or before:2024/01/01