When can I get a custom title?

Um... yeah pretty self-explanitory.

Originally Posted by Newbie's Guide

Ranks
Beneath everyone's name, there is a title. These titles correspond to the post count of the user. Once a user has been a member for 120 days, and has at least 50 posts, a custom rank is awarded.

The ranks are:
» Deku Scrub (Minimum Posts: 0)
» Gerudo Thief (Minimum Posts: 30)
» Goron (Minimum Posts: 100)
» Zora Warrior (Minimum Posts: 300)
» Hylian Knight (Minimum Posts: 500)
» Royal Hylian (Minimum Posts: 800)
» Sage of Wisdom (Minimum Posts: 1000)

That, too, is self explanatory.

This lock is therefore also self explanatory.