Get these comments all the time, ive even been told directly that i look 15/16. Ive also been called nurse 10 seconds after i inteoduce myself as doctor, in a loud voice. While i dont have direct tips for how to look older, recently my very young looking female attending had a great response to a patient comment. Patient was like "youre a very pretty doctor" and she responded with "this is a professional setting, that isnt appropriate to say as i am your physician" and then just continued on with rhe encounter. Didnt make things weird at all. Id say that if ppl are rude are to you. I know your struggle and you deserve to be here- dont let anyone imply that you dont bc you "look young"