Is 13 and a half stone healthy for a 5ft 8inc 19 year old girl?

5 stone 7 is around 77 pounds and in my opinion that is NOT healthy for a 13 year old girl. I don't know how tall you are... but if you're fairly short, then 5 stone 7 might be considered healthy. If you're tall, or of average height then you are not at a healthy weight and you should consider gaining weight. You don't have to go crazy on the junk food. Try to add muscle by eating healthy, high-protein foods so you add muscle and yet preserve your 25 inch waist. However, if you are still concerned about your weight, i would suggest going to a doctor or using a BMI calculator. (You can find BMI calculators online, search them on google). Good luck