They may be far from having learned all their lessons in life--and hopefully are open to the wisdom of those with many more years in similar shoes--but that doesn't mean that can't have learned valuable lessons in ten, fifteen years of adult life. I know I have plenty of wisdom now that I wish I could have passed to a five-years younger version of myself. I don't think writing, sharing, or publicizing that sort of retrospective is necessarily presumptuous. Sometimes young tech personalities are pompous, but there are also plenty of my own peers (and juniors!) that I'm happy to take lessons from.