From the Model Mayhem FAQ:

How does registration and the approval process work?
Once you’ve registered your member account, it must meet all of our requirements in order to be approved to access the site. These requirements are clearly laid out here: https://www.modelmayhem.com/help/rules/membership-requirements

You will need:
  1. To submit a biography about yourself of at least 100 characters
  2. At least 4 pictures that meet the requirements for your chosen membership type.
You can enter these things from your My Stuff page under the Photos and Profile sections.

If you do not have these items added to your profile, you will see this when you click My Stuff:


After these things have been submitted, we send your submission to a selected team of members from all fields in the modeling industry to review your profile and ensure it meets our membership requirements.