How do I remove my birthday from my profile?
You can remove your birthday from your profile by following the below steps:
Sign into twitter.com or open your iOS or Android app.
Go to your profile and click or tap the Edit profile button.
Click the Birthday section.
Change the values you selected in each of the birthday dropdown menus back to the default values (e.g., “Day," “Month," and “Year”) (web) or tap Remove birthday (iOS or Android app). Note: to remove your birthday from your profile on the web, you will need to remove your information from all three of the birthday fields.
Click Save changes (web) or tap Done and then Save (iOS or Android app