Yeah you say this, except there's a good chance you were chronically dehydrated as a kid. The reason you didn't think you were is because a) no one was talking about dehydration at the time, and b) the effects weren't immediately obvious.
But when my grown-up massage clients get on my table and I have to keep reapplying lotion because their skin absorbs the first layer immediately? When they have a million "knots" because their soft tissue fibers got dried out, lost their elasticity and became sticky, basically glued themselves together, and now it hurts when you move your arm like this, or your neck is always achey?
Yeah, that's chronic dehydration. That's shit that builds up over years of not drinking enough water (and/or not stretching, and/or having shitty posture, and/or not healthily processing your difficult emotions, and/or...)
Health is mostly maintenance. You have to act in "healing" ways consistently if you don't want to spend your life in a cycle of pain -> fix -> same pain again. And the younger you start, the better your results will be.
So yeah, treat the youth and yourself like beached orcas and drink that water.
