Hello,my younger brother is 15 and his height is 5 feet 9inch and i am 17 but my height is 5.7...any suggestion?

Both normal: both of you are in the normal range, it is normal to have difference in height between siblings as there are many factory that affect that, mainly genes, as you look different also height and other characters can be different Other factors include nutrition, use of medications and other diseases as bowel, lung, kidney, endocrinological and other chronic diseases

May be too late but: Most men stop growing around age 18- but occasionally some will grow until age 21 or so and occasionally even grow a few more inches. Taking measures to increase your production of growth hormone might help, but if your growth plates have closed then you've reached your max. See http://www.Thebodywellusa.Com/blog/dr-mike-carraghers-top-10-ways-to-increase-your-human-growth-hormone-hgh-levels

Different genetics: Now everyone is unique. Each person has his own unique set of genes that will develop who you are including your height. Now you are very young you are not finished growing and neither is your brother. You are fine just be happy with the way you are

Both heights normal: Both of those heights are normal for average Americans. Most people reach their maximum height in their late teens. Without nutritional problems or chronic childhood illnesses, height is largely based on genetics and parental heights. Aside from eating right, exercising, sleeping well, and being happy, there's not much a person nor his doctor can do to increase height.