I also started dancing at the age of 16 and I know exactly how you feel. Being in classes with people who were much more advanced than I was or thinner than me was a serious challenge for me at first. There were many times when I wanted to quit or give up but one thing kept me going: my love for dance. Even when things seemed unbearably hard, like balancing schoolwork and working on dance, my love for both things kept me going. Try to find your balance and if you really love dance, no matter what the situation or people around you might be like, you’ll keep going.
And remember, practice makes perfect. Keep practicing and you will get better. Don’t compare yourself to the skills of other people because there were once where you were and through practice they got better. I know entering and art form where people start before they can walk at the age of 16 is a challenge, but I have faith you can do it!