Just because we have seen the literal destruction of Sesame Street stuff merch wise into this FP 'Sesame Baby' stuff(look to Japan for the real Sesame collector market)...as well as all those kid's books...I would surmise, just like a lot of the classic Muppets, some of the Sesame gang are adults.
For instance, the Count and Cookie(and I forget what others)
drive in Follow that Bird. Now obviously Muppets like Elmo, Zoe, Tutter, Treelo, Robin, etc are kids. But Grover is questionable...and Bert and Ernie...well, not sure.
Then again it wasnt til a few years ago I realized Bird Bird is spose to be a boy. There is nothing in my endless viewing hours of Sesame growing up that indicated to me he was a boy, but whatever.
To that note...I still say the best Sesame Muppet right now is Telly. It is a **** shame for the performer and Telly fans he's stuck on Sesame...I really think he has this kind of break through potential. I mean because of fan's and peopels perception of Sesame, a lot have either passed up or dismissed automatically characters on there. But Im telling ya, in my book: Telly is right up there with Pepe, Joe the Armadillo, Mo Frackle, and other popular and overlooked characters I feel exude a strong sense of originality and fun.