Except in the case of liquor given to a person under the age of twenty-one (21) years by his parent, guardian, physician or dentist for medicinal purposes, no person shall give or otherwise supply liquor to any person under the age of twenty-one (21) years or permit any person under that age to consume liquor on his premises or on any premises under his control, and it shall be unlawful for any person under the age of twenty-one (21) years to purchase or attempt to purchase, consume or possess intoxicating liquor as defined in RCW 66.04.010 through 66.04.380.