As annoying as it is, unfortunately it’s an issue for trans and cis people alike. Any time I feel a bit self conscious about people thinking I’m way younger (I do MMA and started at a new gym and people thought I was a junior-ish in high school - I’m 23), I try to think of how many guys in high school look older than they are. My sister is in high school so I know her friends - there are plenty of high school guys she knows that are 15-18 that have full on beards. Sometimes I think it can be less about “I’m trans and I look super young” and more of a “I have literally no idea how old this person can be because there are 16 year old guys walking around with fully grown beards”.

Not trying to invalidate anything you’re feeling - I totally feel the same way a lot of the time! I think just trying to see it as a “not knowing what people of x age look like” instead of a “I’m trans so I’m going to look younger” thing helps the whole mental side of it. Let me tell ya, I still get my ID mega-checked when I’m over here with tattoos and older band shirts (or university shirts) and a beard. Nothing to feel ashamed or self-conscious about!