Advice to people of any age, the younger the better.
Decide clearly on what you 'value' rather than what you believe. In other words form a simple mantra; for example mine is Peace, Love, Respect, Cooperation and Harmony.
Choose your words and meanings carefully; for example I do not mention freedom although to me that is crucial; however I find it implicit in all of my values.
Now plan ahead to your deathbed. You want to leave this world satisfied you lived your life as best you could. Contemplate the possibilities of what that could be.
Now apply your values to your words and actions as you go throughout life. Challenge your beliefs, challenge others, challenge agendas, especially those that do not abide by your values.
It is OK for others to have values different from yours, so seek others mantras and values. You may just find them very similar, but the other person may have different beliefs.
Do not fight over different beliefs based on the same values.
Seek truth by observation, not from textbooks.
And if Love is one of your values, spread it fearlessly.