I think people think I am younger than 30 because I dress and act like a teenager many times and feel most comfortable around people age 22-25. My GF is 7.5 years younger but I would be surprised if anyone knew that without being told. I've also seen guys that I though were my age but are still in their late teens! Some kids today have more facial hair than I do.
When I wrote that '30' above it felt weird. I do not feel 30 at all mostly because I am so far behind emotionally and am going through what most guys do back in college.