Yoshimi, thanks for the feedback, but I have to say that, like many 17 year olds, you seem to be missing the point.
You should read Pattie Boyd's biography "Wonderful Today" (or "Wonderful Tonight" which is the American version of the book with basically the same content). She began modeling at age 17, and later became Mrs. George Harrison of the Beatles and then Mrs. Eric Clapton.
She went on a hard diet in her modeling days, and although she doesn't actually mention that there is a link, she ended up having kidney problems and also was not able to have a child. From the book, you can sense that she regrets the diet (although she's very happy with her life now).
Your father is a guy. He seems to put his priorities on "height" which sounds reasonable if you were a male. But even though you don't need to grow "taller" any more, you're a female and you need to maintain your organs healthy. In particular, having a hip too slim is not the best idea for having babies, because if your pelvis is too slim you may end up having a Cesarean like me.
Also a lot of young girls end up having no periods once they go on a diet. Now, this may sound nice considering how annoying periods are, but believe me, when it's not coming you'll miss it a lot. This has happened to me too. At age 18 I went on a diet. I was eating properly, calculating calories and making sure I eat balanced meals, but as soon as I noticed myself "looking good" my periods were gone. I had to go to the hospital to have some medicine prescribed.
Btw, excuse me but I still look great now at 47kg/158cm! Like Ikuyo-Kuruyo, for the first time in my life I'm having very little trouble keeping this figure, and I'm also comfortable with this weight health-wise now. But teenagers are supposed to be chubby. That's how your hormones work, and that's the fat you need. I was hardly unable to go under 49kg in my youth. Then as you get a few years older, you become a bit slender. I have to say I can't agree at all when your dad says that if you wait until your 20s, it will be harder to loose weight. That's quite the contrary, my best-looking days figure-wise was during my late 20s to my early 30s, and I had my child at age 30.
Surely, once you get pregnant, your waist skin expands and it will be harder to get a slender waist. But this has nothing to do with your waist measurement of age 17. 17 is not at all your last chance to loose waist measurements nor your last chance to loose weight. Even if you were to have babies at 19, since you'd be still young, you'll still have the chance to become slender in your 20s.
I can also think of many examples of slender mothers. The current Empress Michiko right after she had 3 children, Jerry Hall after she had 4 or 5 children between Mick Jagger, and many more. Especially, Empress Michiko was slender as a mother than she was as a teen.
And Japanese size 9 pants are quite normal. A lot of fashion designers try to "keep their figure so that they could wear their own size 9." Size 11 can be a bit big, but as long as you're slim on the top, you'll look slim as a whole even when your bottom is big.
Again, try to do excersize that make your waist and legs "tight". Even if your hips are big, as long as those hips are "shaped" good, you'll look great. Look at all the James Bond girls. Have you actually been doing excersize? I hope you are at least working on your muscles before you ever think about cutting down on your nutrition.
Btw, I didn't mean that mucho men don't stretch their muscles. I was just trying to say that the way to prevent yourself from being a muscular girl and yet making yourself turn into a girl in good shape is to stretch. That's what Chisa from Girl Next Door said on TV last week.
http://girlnextdoor.jp/index.htmlShe says that almost all she ever wants to do is muscle training, but that she makes sure she stretches them well at the end of her excersizes.