Hi - The date field UX is difficult for birthdates. It starts in the current month. It is not obvious that you can click the month or the year at the top to set these fields. All users that tested this were clicking the back button to cycle through the months. (If you were 50 years old, you’d have to click the back button 600 times).
Some users did use the back buttons to get to the right month and clicked the right day, then tried to change the year at the bottom, but this doesn’t work. (It can only be changed at the top, which only 1/5 users figured out).