Девочка - it is girl under 18. But we can name and why older, because it is nice and pleasantly. Девушка - from 18 to 35 (i think).

Спасибо

девочка - something between 0 and young teenager, let's say 13 девушка - teenager and up to whatever. We have that strange manner to address all women especially in service as девушка, doesn't matter the age