Not every superhero has the powers of Dr Manhattan or Deadpool, so they get old and worn out eventually. A charming series by DeviantART artist Lelpel plays with the idea, imagining what they would look like 30 or 40 years from now.
Here's some highlights, and the artist has a lot more in his gallery. Most of them would still kick supervillain butt:
Old Superheroes by Lelpel [DeviantART]