Never.... we are always changing, but looking at car accident rates:

There are two periods where there are sharp declines: 19, and sometimes after 26, all the way to 35.

https://www.hallandalelaw.com/wp-content/uploads/2013/07/IIH...

If we assume, this is a indicator 'maturity', then the answer should be around 26-35, depending on the individual. It seems that the founding fathers were into something when the made the minimal age for a president at 35.

There is a reversal at 75+, but this is due to age related issues. And my experience from the older folks in my life, it seems people start reverting to a 'teenage' like state at 75+.