Possible, certainly, but it has a number of issues:
1) MitD hasn't grown larger
2) His personality hasn't changed
3) He's too lazy to gain levels.
But I could accept it in the right suggestion, similar to how dragons gain abilities with age, but in a species that isn't significantly larger with each passing age group.
Do the White Slaad have telekinesis? MitD could have done the transition between pre-white and white, and there would be nothing to be noticed in the comic.
Grey Wolf