I have it very clear ... use condoms.

I'd say: See all those hot guys in high school with awesome packages you really wanted to do:    DO THEM.

When you go camping with Kurt and he asks you in the dark if you want to "play cousin" don't be afraid ... you might like it ... a lot!

Life is a learning process so be open to those fantasies about men and see if that's what you really like.

In the coming years you are going to have a chance to put your penis in some vagina BUT will also have a couple boys hit on you.  You ARE GAY!  Don't pick vagina this time!! Idiot!   

Oh--and track down that Playbuddy guy and make friends with him and have a sleepover... 

Buy Apple stock. Oh wait, I had no money then.

When I was 15 there was a gut named Aidan, 14, and he wanted a regular wank with me. I never sucked him. I really regret that. We remained friends for a few years but then he decided he didn't want to be gay, whatever that meant. Anyway despite being in the same school and seeing each other on a daily basis, I never got to wank with him again. I wish I had at least swallowed him once. 

Let's say you have a 15 yo nephew (or son), what would you say to him?

Don't be such a slut. Lol

"carpe diem, quam minimum credula postero"

("Seize the day, put very little trust in tomorrow (the future)")

btw, in case you were wondering, no, I don't know Latin - I just copied it from wikipedia, though I did remember it from "Dead Poet's Society" ;)

i think this isnt a question to be analyzed --its just a question about if you could go back and tell yourself something what would you tell yourself

You guys are so wrong. Time travels don't work that way, if you travel to the past, that past becomes your future, and your former present becomes the past, which can’t now be changed by your new future. Nobody has watched Avengers Endgame or what..??

Don't play tennis, you'll demolish your ankle and get into all kinds of physical problems.

(i'm overweight, Diabetic with a high blood pressure and a open leg wound that doesn't heal, so losing weight is a real issue at this moment, i wish i could run but i'm glad if i can make it to the toilet and back without pain).

Also: don't invest any effort in Niels, not worth the effort and you'll end up with a 40K dept.

I'd say "Go for it he might like you"

I would say him : become what you are.

"You're homo.  Admit it to yourself, then come out and enjoy it."

I'd say don't let religion stop you from being the person you really are and don't miss out on your teen years due to religious and parental control. Enjoy your sexuality.

Stop hiding. Buy stock in Microsoft. And move to London like you dreamed.

I’d tell myself to put down that cookie and workout. Being fat is a guaranteed way of being lonely and miserable.

Buy bitcoins and Tesla stock !

Get as much sex as you can while you are young.  Try not to pigeonhole yourself into defined roles as your sexuality is constantly fluid.