When you first open an account at YouTube, you have to enter your date of birth. After confirming your details, YouTube shows your age on your profile and updates it annually. If you enter an incorrect birth date and later want to change it in your settings, you will discover that Google, which owns YouTube, does not provide a way for you to do this. You can however change the age that displays on your channel.
Log into your YouTube account. Click on the small triangle next to your user name on the top menu, and select "Account."
Click on "Profile Setup" in the left menu. Scroll down to the section headed Personal Details and under Age, select "Do not display my age." Scroll down to the bottom of the page and click on "Save Changes."
Select "My Channel" from the top menu. Click on the "Edit" link in the Profile section.
Enter your correct age in the "About Me" box, along with any other information you want users to see on your channel. Check the box next to "About Me" to make the information visible and click on "Save Changes."