Prodigy
I don't know what Jim Henson's take is on the maturing of his Muppets, but these timeless characters seem to have grown up with more mature personalities.

Characters such as Kermit the Frog, Miss Piggy, and even their Sesame Street cousins Ernie and Bert, seem to have the same voices and appearance that they did a few decades ago, although their acting careers have clearly taken a more diverse set of roles.