Here's how I think it works.

You can't transfer between 2 different b.net accts, if the account you are transferring (the wow acct IN the actual bnet acct) is less than 30 days old....

But that's not a restriction if it's the same b.net acct.

If you have 2 different b.net accounts - Bnet 1 and 2

Then you create a new wow acct on Bnet 1 called wow 1
and create a new wow acct on Bnet 2 called wow 1

You can't transfer Bnet2.wow1 to Bnet1.wow1 acct until Bnet2.wow1 is at least 30 days old
But you could transfer at any time on Bnet 1, as long as it's another wow acct on Bnet 1

If the wow account, in the battle.net acct is over 30 days old, you are free to transfer to anything...