Talk about getting hit to the head. Check this slo-mo video of a moderately hard hit to the head and then decide if you want this done a multiple times (never mind countless times in your fighting career) to your head - I think the issues really start surfacing when you're old and decrepit as we're starting to see with retired American football players -

Remember you're older for a lot longer than you're young.

Yuishinkai Kobujutsu USA -
Martial Arts with Colman -