Common advice is "learn to be happy with what you have", but that will never work if your dream is to do something Great, for future generations to remember -- to not throw away your shot.
What noticeably cheers me up is reading about all the people who started doing interesting things only in their 30's and forward, or those who reinvented themselves at some point in their lives and went on to be famous only on their second (or third) wind. I wish we had more of their stories instead of the endless parade of young genius entrepreneurs. Learning about the breadth and diversity of human experience is always such a pleasure, and it helps me remember that shaping your life and personality to meet your intellectual goals can be a grueling, decades-long process.
(Incidentally, reading Show Stopper! about the NT kernel was really great for this: although Dave Cutler was clearly a very accomplished engineer at the start of the book, he was in his 40's and experienced mostly in "archaic" technology when Microsoft decided to hire him. This wasn't at all the focus of the book, but it was wonderful to witness the power of a competent mind so quickly and confidently adapting to new technologies and problem domains!)