I'm amazed you weren't able to get more responses to this, but after racking my brain it took a bit to come up with one.

How about Threadless? Though I can't seem to find anything that says when they were founded, I'd guess it's about 3 years, but could be more.

37 Signals didn't taking funding until after they were already successful, and of course they've been around for more than 3 years.