The other kids won’t consider your feelings when they ask where all your hair has gone, but when you tell them you are from the future they will be jealous. They won’t believe you at first, but they will, one by one, as you recount your story; the story of your life. You’ll speed through the cool stuff to make it seem trivial, like how your first kiss is in middle school and it will be with Jessica Marston (who luckily isn’t in the audience) or how you get caught one night in high school driving to a girl’s house at 3:00 a.m. You won’t focus on those details.
Instead you’ll concentrate on why you chose to come back. You’ll tell them that in the future there is a medical procedure that makes you live forever called Chronostatic Rejuvenation, but you will be too old by the time it is available to have it yourself. Then you will proceed to describe your work that helped discover the procedure. About when you worked as a theoretical physicist for CERN focusing on time travel by singularity. They will latch on to the words “time travel” because those are the only words they will recognize.
The stubborn one, Nick, will ask why you’re still a kid if you were old when you traveled back in time. You will answer, in a tone implying the stupidity of the question (a technique obviously passed down by your father), that your consciousness traveled back in time to your earlier body. That is the only way to travel in time because it doesn’t result in there being two of you, thus eliminating any chance of paradox. A side-effect of the transfer of consciousness explains why your hair fell out. He will nod, acting like it is an obvious explanation. The proof is evident after all. No one will disagree because no one will admit they don’t understand.
You’ll bring the story home by explaining that, since you couldn’t be immortal, you chose to relive your life a second or maybe third time. You tell them you can’t remember exactly what number it is to add both flair and believability. They will walk away stunned by everything you have and will experience. They will believe your story so thoroughly that none of them will believe their parents who tell them the real reason you stop coming to school. They will believe you have already been recruited by MIT, as you told them you would be before the end of the year. They will believe their entire lives, because it will be easier than the truth.