Well that just depends on you there is no set age per say. All girls try before they actually need too but I'm glad you are asking - I'd like to warn you if you haven't tried yet.
Watch the pressure you use especially around your ankles and the front of your leg (your chin) wherever there are bones that you know they are there don't press hard. I realize you will learn your own way in due time but I wish someone had of told me that back then! Also, watch any ridged skin such as your knees or back of leg upper heal.