For a quick an easy way to capture clients date of birth on an ipad ensure you set up a TEXT custom field (not a DATE field) and name it 'Date of Birth' rather than entering it inside the contact profile area. See screen-shot example below.
If you are not sure how to set up a custom text field click here for more information.
The reason it is difficult trying to enter a date of birth using the 'date stamp' method is because of the number years you have to scroll back. As soon as you press the arrows too fast the screen would reduce and increase.
Using the date stamp for more 'normal' things such as a month ahead or so would not prove as difficult from an iPad.