According to Pirkei Avos, “Arbaim l’binah”.
I noticed a surge in wisdom at the age of 38. I was assuming that it has to do with the fact that it only takes women 12/13 of the time to get to Bas/Bar Mitzvah, so proportionately it works out about the same (assuming that the surge in wisdom didn’t happen on my birthday).
I have also noticed a fairly steady increase in wisdom ever since. I think it’s connected to life experience.
But some of it could have to do with a person’s particular life experience and what he/she happens to go through at different stages.