Baby dreads... Extensions?
Dread Accessories
It is really about personal preference and why you are on your dreadlocks journey. If you are doing it for fashion/image reasons, then I'd say wait until they are a little bit more mature before attaching extensions.
If you are dreading your hair for a more spiritual/emotional reason, I'd say let your locs grow on their own. As SE said, taking biotin (5000mcg) daily will help your hair grow. It does take a couple months to really start working, but you'd have to wait longer than that to put in extensions anyway, since they won't stay in if your hair isn't locked up enough.
The only thing I will warn you about, is the people saying they crocheted their extensions in....crocheting breaks a lot of hairs, which creates weak spots in your locks. It might not seem noticeable at first, but over time, it can cause your dreads to break at the weak spots. One time crochet might not lead to the dread breaking off eventually, but I wouldn't risk it personally. It is your head, however, thus your choice. I just wanted to warn you so you are aware of the potential danger. I think the bad heavily outweighs the good with crochet needles and dreads.