"When I was a boy of 14, my father was so ignorant I could hardly stand to have the old man around. But when I got to be 21, I was astonished at how much the old man had learned in seven years." -- Mark Twain

As a 38 y/old: You have no idea how much time you have right now. I thought I was always really busy, but looking back I didn't realize how much time I actually had when I was in my 20's. Try kids, your own house, (older) relatives, everyday stuff, a body that requires more 'maintenance',a full-time job and a startup. OP says "money is fuel", but time is perhaps even more so.

As a 31-year old, the main thing I've learnt is that at 24, I knew nothing. Nothing at all.

I imagine I will feel the same way about 31-year-old me, who is at last, finally, starting to Get. It.

Conversations with my 69 year old Dad suggest that he too feels as though he is on the cusp of true understanding.

Also, here's a joke for old farts.

    When I was 18, I actually did know everything*

    * for sufficiently small values of 'everything'