I wanted to be Ernie, but I’m actually Bert.
I wanted to be like Sara Crewe in A Little Princess. She was strong, kind, generous, poised, and spoke perfect French.
As a very young child I would have gladly traded places with Mighty Mouse.
Later on I thought that being Mark McCain (Son of the Rifleman) would be a pretty good life.
Captain Picard has always been a role model to me do to his stoic professionalism among other things.
Anne Shirley. I’m 50 and I still aspire to be Anne Shirley.
Except for all the times you were being held hostage to keep your father at bay, and the deafness that would eventually develop from having said hostage takers shot at close range while standing next to you. 
Pretty much this. Throw in the Lone Ranger, Roy Rogers, and Tarzan also.
Add to that, Superman.
Although I did learn a fight move from watching the Lone Ranger which served me well in a couple of fights - until I came up against someone who also watched the Lone Ranger when he was a kid.
Sky King was also pretty cool, although it was really just the airplane.
Huck Finn
As a little kid, Spock
As a teenager I wanted to be Chris Knight in Real Genius (Val Kilmer’s character).
As a young adult, Jean Luc Picard
Han Solo.
I wanted to be Indiana Jones, Solo was my backup.
As a yoot, I as aspired to be the generic Heinlein male protagonist.
I got better.
Ditto. Some people complain that ST:TNG was “boardroom discussions in space” and dull compared to other ST series, but I actually admired that the characters tried to solve their problems through thinking, discussion and logic. The science was nonsense, but the fact that they were solving problems with “ST science” more often than phasers was admirable to me. Picard was often faced with hard moral choices, and stuck with his beliefs and his oaths even when it was personally uncomfortable for him.
Well, other than the episodes where he didn’t. But it is a TV show. 
Howard Roark. I was a very smart outcast and my grandfather was a prominent architect who lost his career when he stopped drinking. By the time I finished my high school Ayn Rand phase and entered an essay contest I was beyond over that.
I wanted to be like Menolly in Dragonsinger by Anne McCaffrey, able to play basically any instrument brilliantly and to compose. Oh, and I wanted fire lizards, too.
Jim West, Jim Kirk, or Jim Rockford. I clearly had a problem with my given name.
Davy Crockett, Daniel Boone, Bret Maverick, Illya Kuryakin, James Bond.
I would say they were all men of action and adventure, but Bret and Jim were kind of interested in avoiding action as best they could.
Ha! I always aspired to be like The Fonz.
While I was very quiet and shy in grade school I convinced myself I was just being “cool” like the Fonz. If a girl came around that you liked don’t say a word. Just be cool.
Same as you it failed miserablly to help me socially.