Originally Posted by
elcruxio
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.
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.
Getting an HR monitor now and figuring out how to use it to gauge pace is a waste of time. Just take it easy on the ride and take advantage of the food and aid stations.
Also, now is not the time to be breaking in a new pair of clipless pedals/shoes and risking knee issues due to a poor fit. Stick with what you have and if your feet get sore just stop and walk around once in a while.
You're young, you'll be fine. It's analogous to a long hike if you don't ride too hard.