How long is "long enough?"
If you were born to do something that you only got to actually "do" for 3 years of your life, would it be worth it? How about if you were offered the chance to do it for 20 years instead - would that be more worthwhile?
It depends on what that certain something is, obviously, but there are many, many people aged 35-45 who really feel called to do something different with their lives and are always defeated by the thought that it's somehow too late. It may be something that takes a year or more to prepare for and transition to, and in their well-meaning, pragmatic minds, it simply doesn't make sense to start all over again since they're already 40 years into their lives' journeys and have bills to pay and mouths to feed and future college tuition looming.
Why bother, they may ask, if they only have another 20 years left to travel down that new path? What could they possibly accomplish in such a fleeting blink of an eye?
I don't know what could be accomplished by a specific called and dedicated human being in a mere 20 years. But I know that a fireman can save a life in a matter of minutes - don't you think the person that he saved, as well as that person's family and friends, would consider that fireman a success in his career, even if that was the only day he ever worked? I know that Martin Luther King, Jr. changed the lives of all Americans in less than 20 years. And I know that Jesus of Nazareth changed the entire world in just 3 years of doing what he was born to do.
20 years is a mighty long time to make a mark on the world and its inhabitants, even if that world is the size of an elementary classroom and the population is 25 9-year olds, and 40 years old is way too young to give up on a dream.