Earlier quoted context omitted.
Sure, but you don't need first name, last name, phone number, birth date or gender. All of which are asked on the signup and of which only Gender is specified as optional: https://login.yahoo.com/account/create On my small business we ask only for an email address, password and confirm password. Everything else is excessive. Tax obligations can be another problem which may require an address, but often have a simpler…
First and last name at least needed for meet the email protocol. Emails shouldn't be addressed to handles/nicknames
If it's a user experience thing, fine, but at least make it an optional field.