Why are some people smarter at a young age?

Is it just experience? I met my ex in college and he taught me a lot about life... cheating.. abuse.. partying.. deceiving and lying. He also mentioned taking things to the grave and etc... I was still hoping for a fairytale ending with this guy πŸ˜‚πŸ˜‚ i was totally naive

Why are some people smarter at a young age?
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