J37 - I agree with you here. The GP was likely not wrong in recommending circumcision, and in no way is circumcision "routine" at 4.5 years old. It is a medical treatment for a medical condition that the OP took her son to the dr about. OP if you don't want that treatment for your son, that is something you need to discuss with the dr.
I fully support people coming on here for support and personal experiences about medical treatments, but suggesting the dr was wrong in their assessment here is going a bit far.