just enjoy yourself...ignore other people...people who judge you for what you wear and what your voice sounds like, and how old you look aren't worth a fart. forget, just have fun, enjoy your birthday...and the nickname thing works.
You're only 2 inches shorter then me and i have a friend thats 4'9", when people make comments about your height:they dont make diamonds as big as boulders, the best things come in small packages and all that.
The best way to seem mature is not to try, to be yourself, be honest and real...thats maturity, not backbiteing or ********about others behind their backs. have fun, laugh, enjoy yourself. dont worry what other people think of you, if they condem you for external features they aint worth anything, its wot inside that counts and if they believe different, feel sorry for them.
I know its hard to ignore others, but try. The only way you are gonna feel happy is if you feel confident in yourself.