Oh! And just one other thing: this was mainly about younger footballers and it needs to be understood that they are just learning and will head the ball in many unsatisfactory ways before they become proficient. That is when some major damage can be done.
Also, there are different ways of heading the ball; bullet heading and flick heading for two. The first will depend upon speed of impact and the second on how much sideways movement is involved as that will cause the brain to ricochet more.