Nigeria, April 12 -- If you could be one age for the rest of your life, what would it be?

Would you choose to be nine years old, absolved of life's most tedious responsibilities, and instead able to spend your days playing with friends and practicing your times tables?

Or would you choose your early 20s, when time feels endless and the world is your oyster - with friends, travel, pubs and clubs beckoning?

Western culture idealizes youth, so it may come as a surprise to learn that in a recent poll asking this question, the most popular answer wasn't 9 or 23, but 36.

Yet as a developmental psychologist, I thought that response made a lot of sense.

For the last four years, I've been studying people's experiences of their 30s and early 4...