If you lied about your birthday when you started your Twitter account, don't ever update it. Twitter will lock your account until your age is cleared up and that can take months or possibly forever.
Under The European Union’s General Data Protection Regulation (GDPR), Twitter is locking the accounts of anyone who may of posted anything while they were under 13 years of age. If you update your birthday, they run the math backwards, see that you were under 13 when you posted, and lock the account so that they do not get into trouble. It's dumb, but it's the easy way to make sure they don't run into trouble.
Q. Should I update your birthday on Twitter?
Q. What if I have updated my birthday and I am not locked out of my account.
A. You are screwed.
Q. No, really, what should I do?
A. Follow these steps as suggested by Twitter: https://help.twitter.com/en/managing-your-account/locked-and-limited-accounts