I'm 56 now and I'd agree. I bike in the summer for exercise and I drink while on the go as needed. I always got a headache after exercising. A regular headache not a migraine (never had one).

My discovery was Pedialyte it's meant for children but it's like the adult version or Gatorade. I drink it before I exercise and also drink as needed. I feel normal no headaches not dehydrated.

edit: I also have hypothyroidism so my hypothalamus must also be crap at regulating my thirst maybe?