Stress doesn't actually turn your hair gray. That's a myth.
But it will make you lose it.
I cannot disagree more with the "burn through your 20s for the money" notion that seems to pop up with distressing regularity to excuse the increasingly deplorable work-life balance in white collar service industries. While you may technically be able to keep up due to your youth, it is - in many cases - not worth it.
My sense is that this phrase tends to come from those who aren't very familiar with how extraordinarily intense it can be to work in many of the "prestigious" industries that are the endgame for students who actually have a shot at cracking them (think IB, biglaw, start-ups, large corporations, etc.).
Coming from a large-cap corporate legal practice (primarily M&A, financing, and securitization), I know the toll this can take mentally, physically, and socially. It's difficult for most people to understand how soul-crushing these environments can become, particularly when you factor in superiors that are abusive at worst, apathetic at best, and the abundant sums of cash provoking pangs of guilt at every cherished thought of quitting. But know this: it is
never a poor choice to take your life back.
The stress these jobs cause can be devastating to one's health - you never want to get to a point where you can't choose another path, or where all the things you would have made that choice for (health, love, family, friends) have faded from a steady buildup of time, missed calls, and cancelled plans. A lot of posters have already touched on this. Even so, OP, if you'd like more detailed advice from someone who has been down that road, do not hesitate to drop me a PM.