I am 5 7 and a 12/14. Even though I am a quite toned curvy hourglass (32F/30 inch waist, 41 inch hips) I am currently a bit podgy and if I got to the size where 12s were always too small and 14s were sometimes a bit tight and I had to sometimes get a 16, so what I would class as 14/16, then I would definitely be too fat.
It's not just a body image/vanity thing, it's an excess body fat around the middle thing, which is known to be unhealthy.
Most women unless very tall (5 10+) would be fat/overweight at 14/16. Obvious caveats for bodybuilder type athletes etc.
I don't think 5 8 is particularly tall any more. I am 42 and think that women have got noticeably taller over the past 20/30 years.
I reached my adult height in my early teens and used to really notice any women that were taller than me because I saw hardly any. But now there are loads of women that are quite a bit taller than me, that I am now probably at the upper end of average.