This is an easy one. If you don't want to appear in the birthday list, just go to Site Preferences (on the website, click on the cog icon in the upper right corner). You’ll see several checkboxes, including an option to turn off appearing in the birthday list.
From the app, tap on More / My Profile / Edit Profile. Then scroll down to the bottom where you have the "Show up in birthdays list" toggle switch.
Hope this helps,
The Grokio Team