I don't know if this is your first child in the system here but here in the states your acceptance into college is based on 9th, 10th and 11th grades along with ACT/SAT scores. We always pushed the first 3 years and let them take 2 easier classes their senior year. Both of our children committed prior to starting their senior year so this was discussed with the Universities prior. Both schools had no problem with it but they both still took 2 AP classes their senior year.
Don't give in to your son, you are the parent. Don't fall for, "you didn't go to school here" or "this is what everybody does".