How to convince my parents to let me get a new phone?

So I currently have an iPhone 4, which was given to me last year by my aunt, when she got the 5 because she had had the 4 since launch day and I needed a new phone. My phone worked fine at first, but has now gotten to the point where the home button doesn't work have the time, prompting me to turn on the virtual home button, the screen is extremely slow, among other things. My parents, who upgraded to the 4 last year, want me to wait until next June when my brother graduates from 5th grade so we can both get the 5 since it will probably be free, and for some reason will not allow me to take money out of my bank account and purchase a 5s for $100, even though my upgrade came a month ago. I'm not trying to complain, even if it sounds like I am, and I'm extremely grateful to my aunt for the phone.