How can the elderly share what they've learned in life?

First, age is no guarantee of wisdom. Millions, billions of people simply perpetuate what they were taught as children thereby recreating yesterday into tomorrow. So, what older people have “learned” may or may not be “learning,” it might just be repetition of what they were told as children.

Second, I’ll note what I’ve done, for better or worse.

1. Gave all my carefully written and revised annually teaching notes (six file drawers of case files) to my colleagues (digitally)
2. After retirement, wrote a book I’d been collecting data on for 20 years: A Song of Humanity: A Science-Based Alternative to the World’s Scriptures. Including 20 pages of references and over 900 footnotes. Clayton Christensen wrote books. So have others. Whether people buy them or not, is another story. Some people write books just for their families and children.
3. Created web pages to share what I’ve learned with others. Getting Below the Surface , A Song of Humanity , and Personal Web - James G. Clawson Including over 200 video clips explaining the key concepts in my book, Level Three Leadership.
4. Created a blog of my thoughts. James Clawson's Personal BLOG
5. My purpose in life has been “to help others find themselves.” This grew out of my history having had three last names and pondering who I was for long periods of time. To that end, I inherited and developed a career management system that helps people define who they are and how that might be used to assess possible jobs, careers, partners, and moves. See the COW Career Option Workbook on my personal web site above.
6. In retirement, I’ve found Quora to be a way I can continue fulfilling my purpose without teaching formal classes, traveling to consulting clients, and going to conferences. So, this works for me—and I hope for readers.