I want to make a date of birth box in registration and checkout

[Guest superbows]

Hi,

I want to make a date of birth box in registration and checkout, and it to print on on the print invoice.

I want it there to be a box which has seperators, so in the box it looks like this: DD/MM/YYYY (obviously the DD MM YYYY bits are changeable.) But I want it to bring up an error if they put a DOB under 18...

Also, underneath it, I want a check box to say I confirm that I am over 18 years old.

I look forward to any responses.

Kind regards

Sam