Thank you for the YouTube link AndKnowItsSeven
Not being a fan of Britney Spears I was not aware of the use of a title so similar to my - much older - quote. But you still haven't said whether you think the quote is factually inaccurate when applied to a 15/16-year-old girl. Unless you mean this
A 15 year old is legally a child.
Did I say otherwise? But I said words to the effect that the legal status of a young person is not necessarily the same as reality. I was a "child" at 20. Had the law not been changed, both the OP's DD and her boyfriend would legally be children. Would that affect your argument?
Incidentally, in Germany a child is defined as a person under the age of 14. 14 to 17-year-olds are "juveniles".
In the UK, the Citizens Advice Bureau uses the same age limits but uses the term "young people" rather than "juveniles".
I presume you will find this irrelevant too, because it isn't the law here. I happen to think that the law is a bit out of touch with reality, whereas the Citizens Advice Bureau has got it pretty much spot on, based on my own experience of working with teenagers. To give successive governments their due though, they have been gradually giving more legal rights to 16-year-olds over the past few decades, with hopefully more to come.
About as much as the Canadian age of consent
I never mentioned the Canadian age of consent. Do you not read my posts? FYI though, the Canadian age of consent was raised from 14 to 16 in (I think) 2014. But, at the same time, the Canadian government introduced a two-stage close-in-age exemption, as I described earlier. I am not going to repeat my explanation as to why it's relevant because I think most people will find it obvious.
the fact his DS has got a flat in London who knows why thats highlighted
Again, I think most people will be aware that London property prices are high, yet my son can afford to live there despite not going to university. I offer this as an example to the OP (and her DD) that a 16-and-a-half-year-old moving into her own place is not "throwing her life away" as some seem to suggest but, with determination, could actually work out for her. I'm focusing on the positives, whereas you are only concerned with the negatives (and being a bit melodramatic about it, imo).