My brother was about that at 12, of course he's about 6'8" or so now, he's 21. I may be wrong about that, so don't quote me, but I believe he was that tall. I was around 5'7" or so then, I'm 6'4" now at 23. So, I guess 5'9" at 12 is possible, depending on how you hit growth spurts and what not, plus how tall you are suppossed to be when fully developed.