Honestly, I would say if you know you want to use TOG for high school, get it now. Get your feet wet and start getting comfortable with TOG.
We are in our second year with TOG and plan on continuing thru high school. I have a 7th, 5th, 2nd grader plus tag along Ker and preschooler. (Plus adult son, soon to be 2yr old and baby in tummy! Lol)