Let's all agree that hitting your head with regular intent against anything motionless or moving, no matter what the force involved, is never ever good for any person's head.
Whatever age or stage your brain is at, the skull can only offer a certain level of protection. Every time the skull is rocked and shocked the brain bounces around inside it causing bruising, however minimal, to the most precious and irreplaceable organ we have. This is just basic physical fact. And, believe me, I'm not scaremongering. I'm just explaining it best I can so we can also look at finding a solution if there is any. And, thankfully, I believe there is.
Like most things, when you remove the hysteria from around the issue, the answer is often equally simple. Approach it in the right way, which means not getting kids having hours of heading practice two nights a week, teach the proper technique and it will be fine — just like teaching kids the right way to tackle in rugby. Be sensible, be practical, be aware of it, keep an eye out for it and use your common sense.
Heading a football by definition shouldn't be that good for you, but if done right probably also isn't that bad. Just like the game itself, it's all about being smart and using your noggin.