I'm sorry but THC is absolutely not recommended for the people under 21.
I've seen several bad cases with neuro/brain development gone super bad exactly because of smoking too soon and too much. Lost few friends, I know what I'm talking about from the experience. I know that young people say that it is none of my business but the odds the get psyhosis are against them.
Otherwise, the effect is always personal. You might be well until the end of your life or you might trigger some weird neurological disease at some point.