That is dependent on a variety of things. You are not severely underweight, and you are young. The BMI is intended for adults and is not always appropriate to younger adolescents. Its applicability is determined by your tanning stage.

As a result, if you are not in Tanner stage 5, you are not necessarily underweight. The other problem is what you consume. Are you dieting or are you naturally thin? What is the nutritional quality of your diet? Are you receiving enough protein, calcium, and vitamin D through your food by being outside? Exercise will also be an influence. If you are engaging in weight bearing activities, even if it is as simple as walking the dog.

It takes severe starvation to have an effect on height. Height is determined by genetics. Chronic, moderate to severe malnutrition, generally beginning in childhood, can have an impact on your eventual height. Being slightly underweight at 14 will have no effect.

However, if you don’t receive enough protein, calcium, vitamin D, and weight-bearing activity, your bone density will suffer in the long run. The solution is to eat healthier and move more.

You can calculate your BMI here

How do I know if I’m malnourished?

If you’ve been sick and haven’t been eating correctly, or if you’re underweight, ask your doctor about a brief questionnaire called the MUST tool. In my work, I frequently find that family of elderly loved ones are the ones who raise this as a potential concern. If you’re worried about a loved one, use the MUST score to assess their risk and consult with their doctor if you believe they’re at danger.

The ESSENTIAL score
What is your body mass index (BMI)? (above 20 = 0; 18.5-20 = 1; and less than 18.5 = 2)
Have you lost weight unintentionally in the previous 3-6 months? (under 5% weight reduction gets a 0, 5-10% gets a 1, and more than 10% gets a 2).
Have you been really ill to the point where you haven’t eaten anything for at least five days? (This happens seldom unless you’re very ill and need to be admitted to the hospital, but it earns you a 2 if you say yes.)
If your total score from stages 1-3 is 0, you are at low risk of malnutrition; if it is 1, you are at medium risk; and 2 or higher indicates that you are at severe risk.