There are milestone markers for children to measure their progress - their first smile, when they're able to roll over, etc. There are also "milestone markers" for more advanced ages, as well. And I haven't seemed to have hit any of them.
While most people learned to drive in their teens, I didn't learn until I was 27 years old. While the average age of a college graduate is 22, I'm still working on my Bachelors degree at 48. While most friends my age have been married quite some time, have children and even grandchildren...well, we know where I rank there.
I'm overcome by a sense of never ever being able to catch up. I'll never reach "my full potential"; my life is half over and it's never really begun.