Sooner, I was in the same situation 2 years ago with my (then) 12 yr old son.... He had outgrown his smaller bow, but not strong enough to pull an adult bow....
I went to the local pro shop and picked up one of these:
Diamond Razor Edge
It has an adjustable draw length of 19" - 29". The draw wieght on it is between 30# and 60#. More than enough to last my son until he's 18 years old....
It also came as a package, ready to shoot (just needed arrows). All for about $350 (I think)
(Hell, I might even set it up for me as a backup bow)
J.