Am i naturally skinny?

I am a 16 year old female and i weigh around 106lbs and i am about 5ft 7 in height and i eat normally breakfast: crunchy nut cereal, lunch: ham salad baguette and a strawberry milkshake and for tea: chicken dippers and chips and snacks: strawberries and icecream, hot chocolate btw this isnt everyday just an example of a day. I dont seem to be gaining any weight and do i have a fast metabolism or something and will i gain weight when i am older and why is my body like this ? thanks