I'm 26 and but I look much younger (as long as I shave my beard). I regularly have to show my ID when buying alcohol for instance (which you can do with 16-18 in my country).

It's rather fun for me and I enjoy these kinds of interactions. Can't say it really ever hindered or embarrassed me in any way.

I suspect that if those people who feel embarrassed because they look young were looking older, they'd find something else to be embarrassed about. It's easy to find any number of shortcomings with yourself.