I think the people who need to hear this message are not in their late 40s, but are in their 20s thinking that they have to do it now or they never will. I see a lot of ageism on X from people who are clearly young and inexperienced, but when you actually get into the real world and how things are done you see the vast majority of real success happens later in life once you've been around a couple times.
Experience, on the whole, really does get you further than cleverness, but good luck telling that to the inexperienced.
Something we definitely lose when we age is lack of judgement, and with it the ability to play and experiment. I miss that naïveté and over confidence from my twenties knowing I was allowed to screw up.
Is it really those things, or is it that as we get older we have something to lose? I could go live like I'm 20 again...reduce my spending to nothing, work all day on whatever I believe in...but that would cost me my family's comfort, and I rather like them.
Experience, on the whole, really does get you further than cleverness, but good luck telling that to the inexperienced.