Im a little confused over the feet/inches length of kid and cm length of skis. Im not going to sort it out now but let me respond to your Q anyway! No, let me check........................ 145cm.
Iny123, take your sons length and just subtract max 5cm and you should be ok. Next year he might be 5-10cm taller but for those SX11's length really doesent matter much. If they were SL skis like my sons they could be even shorter.
My older son is now 8y old, about 140cm tall and skis on 121cm long Head iSL RD Jr skis. These skis dont get any longer than 166cm so that leaves us with 45cm of growth margine for the next 8y. Approx 6cm/year untill 16y old. Im 190cm tall myselfe and all the curves suggests he will become the same. When I swapped his old 130cm foam core kidds Elans for those 121cm solid sandwich race department racing skis he became instantly much much better. The change was dramatic.