I have been out for so long that I don't know such details as contribution levels, but I would guess the young don't contribute that much as a group. But they are thought of by the org. as the future contributors, as the old ones die off, and no doubt the org. will be guilting the young earners to contribute more.
When I was young, and also a Reg. Pio. for a while, my thinking was the same as yours, plus I only had enough to live off by Part Time working, to run a car, run a girlfriend, she was always skint, and to have a bit of Beer Money.
I shall be fascinated to see how all of this goes for the Org. To a degree they are being unusually reactive, looking to the near future at least, but I wonder if any of the measures they take will stem the loss of members due to the less obvious stuff, like the spreading availability of easy Internet access around the world, improved Education, and how Society in many Nations is increasingly seeing no need for organised religion in their lives, also the relaxing of things so much will make it much easier to "fade", either deliberately or unconsciously.