That does seem pretty goofy. To even begin getting legacy XP, one character must complete chapter 1 of their class quests. I'm not sure there is a way to complete chapter 1 before level 10 (if you can do it, you have my respect). Chapter one is generally completed in the low 30's.
So if you have legacy level 10, unless you delete characters constantly, you should have a character at level 10.
Since 1.5, Legacy is unlocked at level 10 instead of at the completion of Chapter One.