Facepalming is the act of approaching the palm to your face, it's meant to communicate a deep sense of disapproval and it's a commonly used practice all over the internet foreveraloners and memegenerators.
You can feel free to facepalm whenever you please, it's safe at any age as long as you don't facepalm too hard.

Before starting with yout facepalming activity, ensure you have your caps-lock turned off - it's commonly known that facepalming while caps-locking could cause you some headaches... just in case, turn it off.