The answer is 20 years old. I bet you were shocked at that. I know I was when I first heard that. Every year we lose 1% of our collagen. When you get to be 40 you should be well on your way to a good skincare routine. If you would like more info on how to have a good skincare routine and balance call for a free consult anytime. 519-542-0079 We are always happy to help.