Hello,i made mistake with Apple ID of my older son.I putted birthday year of my younger.I would like to change that .Thank you .

To change a date of birth to any age below 13,* you must be a member of a Family Sharing group, and your family organiser must approve the change. After you've changed the date of birth to any age below 13, you can't edit it.* Find out more about Family Sharing. 

1. Update the date of birth.
2. Follow the onscreen steps to send an email request to your family organiser.
3. Your family organiser will get an email with instructions on how to approve the request. 

*Age varies by country or region. If you need to change the date of birth for a child, contact Apple Support. 

if your son is older then 13

If you need to change the date of birth for anyone below the age of 13, please contact Apple Support.*

On the web

1. Sign in to appleid.apple.com.
2. Select Personal Information, then choose Birthday. 
3. Update your date of birth, then click Save. If you want to change the date of birth for a child, find out what to do. 

Depending on how you created your Apple ID, you may be required to provide additional information or change your Apple ID username from a mobile phone number to an email address.

On your iPhone, iPad or iPod touch

1. Go to Settings > [your name].
2. Tap Name, Phone Numbers, Email. You may need to enter your Apple ID password.
3. Tap Change Birthday or Birthday. 
4. Update your date of birth, then tap Done. If you're changing the date of birth for a child, find out what to do.