1. Sign in to your G Suite control panel at admin.google.com
2. Enable the premium feature for Google Plus, To do this please:
a. Click on More controls at the bottom of the screen.
b. Click on the Other Google Services icon.
c. Click on the Filters icon on the top right corner of the screen.
d. Untick the box next to Show top featured services
e. Scroll through the complete list of services until you find the Google+ icon.
f. Click on Goolge+ icon, this will open the Google+ page.
g. Click on Preview premium features which will open a side view, click on the Preview premium features button.
3. Next reopen the user account information page and you will be able to correct the date of birth, which will unsuspend the user.
For more information regarding Google Plus premium features, please visit this Help Center article http://support.google.com/a/bin/answer.py?hl=en&answer=2677443.