I Eat A Lot But Dont Put On Weight Why?

Some people can eat and not gain a pound. Doesn't mean your not healthy. Not to worry and don't worry make sure you eat healthy though cause it does catch up to you as you get older.

You have a overactive thyroid gland.  Thyroid hormones regulate your metabolism.  Basically, you digest and process food fairly quickly and have a high metabolic (fat burning) rate.  So long as you feel healthy and have high energy levels, it is safe to assume that you do not have any issues with nutrient absorption, your body just burn a lot of energy, even at rest.

People with overactive thyroids are not in danger of anything, although they may not notice a bad diet catching up with them as much as a person who gains weight easily.  Typically, our metabolism slows as we age, resulting in less fat burning and more weight gain.

Eat healthy, as there are many other factors than weight gain that can result from a poor diet.

Because you are super-lucky lol!
Probably you just have a high metabolism. Good for you!

Dietdiva is right, you most likely have a high metabolism that helps your body lose weight fast and hardly put any weight on.