Having been in your position, I understand that having built a product from the ground up makes you feel like you are qualified to do anything. I was lucky enough to get hired at a late-stage startup after my endeavor failed, and am constantly reminded that time in the industry matters. Two years of intense coding is worth a lot, but you've only been exposed to a limited set of problems, both technical and business. 6+ years sounds reasonable to me if they are looking for someone with well-rounded experience.
Mind you, as someone else mentioned, some folks spend 6 years in the industry and don't gain the knowledge and experience you already have, but that doesn't mean you've attained 6 years worth of knowledge and experience.
Mind you, as someone else mentioned, some folks spend 6 years in the industry and don't gain the knowledge and experience you already have, but that doesn't mean you've attained 6 years worth of knowledge and experience.