Although he was forced into maturity in the last two books he was a very immature character and acted very childish. Ron joked around a lot but he never insulted people to the degree Malfoy did. Malfoy didn't understand the world around him. He was incredibly immature.

Hello, the whole I killed Sirius Black thing and the kicking glasses off the table and alot more.

^ i agree. Especially considering Bellatrix is older than the others :D

That too

I don't think Bellatrix is immature. She is simply like that. Crazy. Love her. But second most immature is Ron. And I don't think Draco is immature at all. He, as Bella, is just like that too.

or goyle. Bellatrix isn't really immature, she's more crazy than immature

A bit.
and Draco,too.
I like them,but they are SO immature

I like them both too

bellatrix isn't really immature, just crazy, and i love it! draco isn't really immature either, he was just born and raised that way

Ron is pretty immature