How old should you be to wear make-up?

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I was astonished Friday as I went to my son's kindergarten class. I walked in and was greated by 19 children. Two of which were little girls wearing makeup! I am a firm believer that age appropriate items are much better for a child then allowing them to choose by themselves. When I take my son shopping, he isn't allowed to purchase most items unless they are within his age group. Why should you allow a six year old to wear makeup? My sister in law is 14 and just got to start wearing "some" makeup, mainly eyeshadow and lipgloss on her 13th birthday. How old is old enough? I strongly feel that 6 years old is entirely TOO young! What do you think?