Why don't you want to create accounts through a mobile app? I did the same for Instagram using swipe into DOB area.
In browser with a mobile user-agent I couldn't register.
Im trying to figure out a way I could select the month, date, and year but I dont know how I could do it as the elements all are the same so I really have no way to my knowledge on how to select them. If anyone could help that would be awesome :)! Below is a picture of it. Also this is using a android fingerprint.
