Underdeveloped Body

I am a 17 year old male, but concerned about my body size, too small, rather than too large. I weigh 48kg/95lbs now 5"6 (which is small but not greatly under average as other statistics), and my waist size is 28 inches, and my chest size is about the same as an average 12-13 year old. There appears to be some muscle development but my arms are extremely thin, and a man's hand could probably form a ring around my arm near the shoulder (although not my hand). I am well below average in average body strength although fitness is about average. My main concern is my weight and overall thinness and whether this may have more serious implications in the future. I eat normally (in fact more than most people) and my diet consists of less fatty and "junk" foods than the average diet.
I am unsure whether the factor of late pubertal development has affected me, since I only started significant development at 15, although from then developed relatively rapidly, and have undergone most of the major changes. You may say that it may merely be variation of size, but after several friends' concerns over my small size and no other similarly aged male of my size, I wonder if it is a problem, or simply late development.