For the love of the random deity get a HR monitor. With that you can control your speed better so as you won't be riding too fast. Remember, it's not the distance that kills you, it' the speed. With a low enough heart rate your body won't eat in to the good stuff instead of fat. Specifically your body will use fat as a source for energy (which is abundantly available) rather than carbohydrates (which aren't).
Secondly, hydration is of paramount importance. 1-2dl every 10-15 minutes. Without water you won't finish.
And go clipless. Clipless pedals reduce fatigue and are safer. And since you are so young you'll learn to use them in a day.
Whether you can or can't do it... Well sir, I say you can and will do it easily. Just don't ride too fast.