Probably from about age 12 to age 20 is where there is the biggest physical variation between an individual and others in that person's age group. Don't compare yourself to your friends. Your boobs will come from your genetic package, probably at roughly the same timeline as your mom and your grandma. Try to be patient! There is nothing wrong, your body is just doing what it wants on its own schedule.
I'm sure you're a very beautiful 16 year old : please remember breasts don't define your inside and outside beauty nearly as much as you think : acknowledge that your hyper sensitive to this and try not to focus on it : allow mother nature to take it's course, and regardless of the size of your breasts recognize your true beauty. I just watched Tyra on Ellen, and they were talking about minimizing whatever flaw you think you have and focus on flaunting the other parts of you that you do think are beautiful - maybe your eyes - treat yourself to a liner, your small feet, maybe a new set of tights ? etc. YOU ARE BEAUTIFUL
Here is the good news and bad news. Breast size does change over time. :>) You will be larger down the road, for example, if you have a baby. Get yourself some of the bras with lining and pads. They do a lot to enhance the cleavage these days. hugs
There's not really any particular reason why they're not growing it's just something in your body make up. Some people's breast grow really big and they end up with double ds and then have to get a breast reduction because of all the back pain. They would say that you are lucky that you can move your arms around without bumping into bricks on the front of you. I have four girls, my oldest has big thighs and small breasts, my second has small thighs and big breasts and the third one has small thighs and small breasts, the fourth one is still too little but we'll find out soon! My mom and both my older sisters have always had bigger breasts than me even though I breastfed five times and they only two or three times each. They've proven in science that every woman has the same size and number of milk ducts in their breasts the difference in size is just simply the fat content difference. With the stereotype of being skinny being more attractive I don't understand why people frown at fatless breasts. I once heard an old man say if it's big enough to fit in your mouth then it's perfect. Personally, I like having small breasts, bras are easy to stuff if you want your breast bigger but if you have big breasts you can't just take them off and hang them on the end of the bed at the end of the day!