Love the look and feel of the application but providing some UX feedback. On the initial page the birthdate selector confused me. It took me a while to figure out how to actually get a valid input so I get the button enabled. I think part of the confusion for me was the year chips above the selection, as I didn't realize they were quick selections.

I was trying to select the year I was born, and then click on the year chips, which I now understand reset my selection but it wasn't clear to me what it did.

Once I realized I selected the right year and left the chips alone, but the button stayed disabled. I didn't want to provide the exact birthday. But I realized I had to click on the month to get a valid input.

Just sharing this friction. The input looks nice, but might be a bit form over function here... Consider following typical conventions on how inputs like these work.