I think it's hard to find to find characters that strictly fit the definition of this because really, they should be created by and pushed by the same person. I would say Jessica Jones under Bendis sort of counts, but her own series aren't successive displays of impressive feats so much as they are about her life being mostly shitty, and even when she joined the Avengers, I don't feel like she got to do that much.
Kate never really seemed like she was exactly the same age as the other Young Avengers since the moment she was introduced in Heinberg's run. She was a bridesmaid at someone's wedding, it made her seem more 17-18 than 15-16 like the others. Gillen's justification for making her 21 in his YA was that she seemed older than the rest of the team.