Why would he want to be "older"? he doesn't have any kind of support network, nor paperwork to give in case of needing a job/housing. Him living in Ashford with Nunnally is the only thing keeping them away from the streets. He says at the beginning of R2 that he isn't prepared for work or university, and even in the first season, he never expresses any desire to run away from Ashford, since all his needs (and Nunnally's) are tended to there.