Blonde kids are not usually blonde adults. Bleaching hair is generally how we get blonde adults.

Eventually maybe it will get white, though.

I would say go out more.

Stop getting older. Besides that, not much of a chance I’m afraid.

Hair color changes with age. My mother in law and wife were both blond when they were kids, but their hair slowly turned browner with age. They both highlight their hair to split the difference.

We have two fairly young kids. Their hair is pretty light blond on the top layers, but their bottom layers are quite a bit darker. I suspect the biggest contributing factor beyond genetics is sunlight. Both of them spend a pretty good amount of time outdoors when the weather permits.

Depends on the cause. Genetics/hormones, hard water, buildup, damage, all have different strategies.

I have auburn hair (the red equivalent of dirty blond) and fear discoloration (spots becoming neon red) if I’m not wearing a bandanna. If that’s the reverse of what you want, seek the sun, eat foods that maintain coloration, and avoid certain medications (though are you really going to do the last two things just for blonder hair?)