how to change my age on an apple watch

i turned 13 a few weeks ago, but yesterday when i was looking at my settings i noticed it was still set to “under 13 years old” for the activity app.

i changed it to over 13, and now it tracks my calories instead of minutes, but now i think its inaccurate. i did nothing all day (i pretty much just sat in class for 7 hours, all the moving i really did was about 5 minutes to walk to our next class), but it said i moved worth 200 calories. but when i exercised for 45 minutes, the move bar only went up by 3 more calories.

i want to change it back to under 13 version, but the setting isn’t there anymore. is there a way to change it back or am i stuck with this version of the activity bar?