Does anyone else look younger than their age? I'm 24 and people constantly wrongly assume my age and won't serve me in shops. >_<

Absolutely! I'm not quite 24 (I am in march) but I even got ID's for super glue when I was 21!!  I honestly used to get my friends to go in and buy things for me so I didn't have to go through the stress of taking my passport as I often leave it behind!! But I know how you feel it's so annoying 

People tell me you'll appreciate it when you're older - I don't know if this is true but we can hope!!