Richard, девочка - girl (a child) девушка - a young women. There is not an exact border between two. I think after puberty one can be called a "девушка" but she is still a schoolgirl at that time, so a child, "девочка" as well. Similarly, there is not a border between девушка and женщина, it much depends on how woman feels about this herself. Девочка can also be used affectionately. Also it happens that a lady in her 60s addresses her friends "девочки" (if their realtions are informal)

That is right!!!

Hi Richard! If I need appeal to woman who’s age from 16 to 30 I said «Девушка, извините, не подскажете...». If I need speak to woman who’s age older 30 I said «Женщина, извините не подскажете который час?» If I need appeal to girl who’s age younger 16 I said «Девочка, подскажи пожалуйста, где твои родители?»

Sometimes they can be differentiated by virginity: girl/youngrove(девочка/девушка) - virgin, woman(женщина) - not a virgin. Similarly: a boy/younker(мальчик/юноша) is a virgin, a man(мужчина/мужик) is not a virgin. But it's all conditional ^^