Young or old women who are into prostitution are in it as a matter of choice, just like any other profession, they're in it to offer services and get paid at the end of it, they can choose to do another kind of job and get paid more or less. Although some prostitutes can claim that it's a lack of well paying jobs or poverty that compelled them to enter into prostitution, but the fact remains that there are other women that we're in a similar situations like them but choose a different line of work, so it still comes down to choice, they probably think that prostitution is less tasking with a better pay than probably working in a factory or working as a maid. Unless a young woman is compelled into the act of prostitution, maybe in the hands of sex traffickers, then pushed into forced prostitution. It's important to note that the trafficker can be a man or woman, while the victims are mostly women.

As Hispo, pointed out, if a girl is in a relationship because of material gain, that can not be categorized as prostitution, it'll be called a golddigger, because she's not engaging in sexual acts with every man that offers money for her services.