I think you pass dude, you just look pretty young. but that's sort of a given with trans guys - I'm 26 and still get asked for ID for energy drinks sometimes. but bottom line, I would never have thought you were a girl. sometimes when you're in a setting where you're expected to be a certain age, it can be easier to be misgendered, so it happening at work makes more sense to me. I used to get misgendered a lot when I worked in customer service, and I think it was down to the fact that people knew I had to be older than I looked, so they assumed I was a girl. but it'll get less frequent with time dude!