This post is about the steps required to turn off the friends request received from Game Center on iPhone 4S
Step 1: Press the menu button on iPhone 4S and tap the Settings icon.
Step 2: Tap the General Settings in the Settings screen.
Step 3: From the list of available options on the General Settings screen, tap the Restrictions option.
Step 4: Scroll down the Restrictions settings and turn off the Adding Friends feature available under Game Center section.
Now you will not have the option to add friends as well receive friends request from Game Center on iPhone 4S.