i started a site based on asp.net MVC 3 and MySql i got the membership to work with the MySQL .NET connector so with the default application you get with a new project of mv
Suppose you want to create fields for Age and Gender. you can first of all create UI for registration in the corresponding Registration view. it means creating input fields for Age and Gender. then in the AccountController go to Register view and add Age and Gender fields in ApplicationUser object (that is already declared). And there you go.
Detailed information on this can be found http://blog.falafel.com/customize-mvc-5-application-users-using-asp-net-identity-2-0/