I do have felt similar shift around that age, but I wonder if it is due to reaching certain points in career where you are put into more leading position and have more confidence in what you do even if you don't have children? Easy to go into horoscope style confirmation bias here though.

Nonetheless I am never going to stop saying I still feel like I am 16. Just more confident 16.

As some point you're going to stop saying that because you'll realize that sixteen year olds are generally dumbasses.