Here is an excellent report on how to improve the skill of drawing one girl, who is now 18 years old. His first attempt, she began at the age of 9 years. See more
Age - 9 years
Age - 10 years
Age - 11 years
Age - 12 years
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Age - 12 years
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Age - 17 years
Age - 18 years
Source:
www.savannahrcb.deviantart.com