I'm also 24 and youthful looking. I got ID'd for night nurse yesterday. I get people telling me how young I look all the frigging time. It's just my face/build. I don't let it bother me, as I will have the last laugh when everyone enters their thirties (tired cliche, but true). However, the 'oooh you look soooooo young!!!' comments are more acute when I wear flat shoes. I'm not suggesting you wear heels permanently, but I thought it worth a mention. Also, when someone speaks to me in a patronising way which would indicate they assume me to be in my teens, I find it pleasing to use my over-the-top posho phone voice on them, preferably with obnoxiously long and unnecessary words. Again, that's just me.
As lame as it sounds, everyone has things they dislike about themselves. There's not really a whole lot you can do about it except EMBRACE your youthfulness. Not very helpful advice I know, but bar having a face transplant and/or taking up heavy smoking to encourage the wrinkles, the only course of action is to try and be happy being you.
P.S. I do have a boyfriend who is two years older than me. Fairly sure he's not a paedophile.