Of the 7 main characters, only Leonard and Penny are adults. They both display plenty of immaturity of their own, but they do so within an adult framework. The others are all case studies in different forms of infantilism:
[ul]
[li]Amy Farrah, socially stunted in girlhood, trying to get caught up with female socialization by looking up how-to instructions on being a girl.[/li][li]Bernadette, talking in a squeaky little-girl voice.[/li][li]Howard, still living with his mother and under her overbearing thumb (at least until recently).[/li][li]Rajesh, with a childlike naïveté that has him finding joy in silly trivial things.[/li][li]Sheldon, whose entire personality is motivated by the extreme narcissistic egocentrism of a 2-year-old, writ large.[/li][/ul]
Leonard and Penny are there partly as a foil to provide an adult perspective, the better to set off the infantilism of the others.
This warranted its own thread?
My impression of BBT:
“Bazinga!”
Wait, Bernadette isn’t an adult figure because of her voice? What the who now?
Bernadette seems to me to be the most grown up of the bunch.
I was going to say, Bernadette actually seems the most adult of all of them to me.
ETA: Ninja’ed
While I don’t disagree, it’s my impression that just about every sitcom ever made trades at least in part on the emotional or behavioral immaturity of members of its cast. I mean, that’s one of the fundamental things that makes it funny.
What is interesting is how Leonard’s character has grown, much more than the others. Watching re-runs in syndication, Leonard was very self-aware and embarrassed by his nerd-dom, especially in front of Penny. He seems far more comfortable in his own skin now.
Exactly. She has a little girl voice because she is a tiny little mini-person. With a lot of hotness bursting out of that little package. Hmmmmmm
What were we talking about again?
Certainly she’s passed puberty. 
I must say I also can’t get behind Bernadette’s character as displaying infantilism, but I like the theory, so maybe we can compromise:
She is the playful mid-way that juxtaposes the two states, adulthood and childishness. She looks like a sweetie, sounds like a sweetie, but it’s deception because it turns out that she can hold her own when she suddenly puts on her screaming voice and puts Howard in his place.
Even Howard’s mother is rather infantile.
I’ll second this.
Where the how now?
During the first few season he definitely wouldn’t have snatched his make-up back from her, that’s for sure!
If you don’t think a thread is worth participating in, don’t participate in it. Coming in and dropping comments like this can be considered threadshitting.
Don’t do it again.
twickster, Cafe Society moderator
And in that same recent episode Sheldon actually showed some growth and realized how they look to other people. I never remember him being that self aware before.