Earlier quoted context omitted.
And poor people just should eat cake, I know.. For real, I believe most 17 year olds on this earth do not have the funds to invest in education AND in a retirement fond, so there are choices to be made. (there are also the choices of creating social bonds and investing into activities together, ...)
The root comment was talking about investing 5% of their earnings. If you're making any kind of income at 17 (which admittedly is not everybody) then learning to save+invest a small portion of that can have incredible positive snowball effects beyond the compounding itself. I can't imagine a scenario where at 55 years old, you would miss the 5% of your summer income you invested back in high school. But I can totally…
If those 5% were the question of whether to go with the group on a adventure together or not - and you end up alone at 55 years and not invited .. you might have rather invested different back then. But on the other hand I don't think those 5% of earnings with 17 make a difference later.
The only real difference they can make, if they made you start a habit of saving income for important purchases. (But not really fore retirement at that age. But each to his own)