I guess девочка becomes девушка with the conclusion of puberty.

девушка -- teen girl or young woman; девочка -- child of any age below. Also, девушка is a common neutral form of address for an unfamiliar young woman (and 'young' might be a very relative term in these cases).

things are how previous answers describe, but there is slang still , and in slang they can call девочка a female person until may be 25 , it is in common enough last years, it works like speaking about third person , or addressing in plural

девушка - girl (fille), девочка это скорее - kid girl (jeune fille), но не обязательно. Так что, девочка скорее всего подразумевает маленький возраст

To add to the information posted above, sometimes word "девочка" is used irrespective of age. For example, a husband can call his wife "моя девочка", showing his love and tenderness. Also females usually call their girl friends "девочки" irrespective of age.