Reminds me of movies involving time travel
Please note I tend to be quite different from the majority in many things I say, but here is what I would tell my younger self:
"Learn to rely on your self and your own experience more than on any book, trend, fashion, mentality, culture, philosophy, model of reality, lifestyle or standard of values that exists outside of you. Remain indifferent to the experience of others, as yours can be completely different.
When you're unsure and looking for advice from others, follow the option that is based on the most ideal assumption of what you think would be ideal.
To make your life simpler and your mind independent of others, don't watch TV, stay indifferent or oblivious to popular culture, and in general, use your own mind when making judgments.
Try and live as healthy as possible.
Don't get tangled up in debate, but lead by example.
Don't wait for the approval of others but persuade through results.
Don't be distracted by naysayers while you pursue your dreams.
We are the creation, or rather "embodiment", of an entity approximately described by Christian tradition as God, but present in numerous alternative reality models which may or may not be accurate. The Orthodox and Roman Catholic Christian allegories of life match reality as closest as possible.
While their role in history is marked with much controversy, many parts of their original message permeate consistently in the pattern of leaps of scientific exploration and discovery.
Atheists are good thinkers but often dogmatic in their core beliefs about the unexplored and unproven. The agnostics are generally more consistent with the current stage of scientific exploration. Much is yet to be defined.
Just like the opportunistic Christian false prophets, also worldly populists use rhetoric and inconclusive data to spread propaganda on atheist views. Of course, none of that is science but pure ideological dictatorship inspired by a largely competition-oriented capitalist society.
Our increasingly atheist world places much importance on what feels good and what gives pleasure to the senses.
Don't be deceived by what seems to bring pleasure, don't be deceived by appearances.
Our entire human history was built on sweat, creative thinking, defiance towards the establishment and continuous evolution of our mind. Do try to figure out how come some people equate the promotion of shagging around like primates (promiscuous behavior) with evolution - whether as a species or as individuals.
Many of the arguments of populist atheism are flawed, or at LEAST unscientific.
Relativism for example: how can there be multiple factual truths?
At most, they are multiple interpretations, but not truths.
In time you will find a greater truth built in faith.
Because it was faith, boldness and courage that evolved our society and keeps evolving it, brought progress in values, technology and health - not the cynics to whom sex and booze represent the ultimate purpose of life!
Learn to love, love even if you are hated. You will discover many unexpected surprises when those who hate you know you love them."
(end)
This is what I would tell the teenager I used to be around 10 years ago.
I wonder whether he would take any of this seriously

But somehow, life made him become who I am today.
I am proud indeed.