Look at your wrists. They are slimmer than a man's wrists.Not really. If you are purely like to like, height/weight/development, when he was 12, my son's friend's categorization probably would have had some 14-15 year old girls in it. Now, it probably has some 18 year old girls in it. Most girl's though would be really far down the totem poll of development ranks once the teenage years kick in.
But again, sports really isn't all about fairness and having like to like compete against each other. It's also about participation. Which completely blows apart your argument since you have to therefore ensure the trans also have a place to participate (which isn't necessarily the cis men's division, as we've already established).
Here's a story for you. My son did a winter GK over this last Christmas holiday. The first 3 days he was assigned to a group consisting of mostly older boys in early highschool, a few of them MLS academy keepers, and the two girls in the group were seniors/juniors in high school. He was over the moon and loved the competition even though he was on the weaker side of the keepers. The 4th day the MLS academy keepers had to travel for MLS responsibilities of the weekend and so weren't at the camp. Several girls his age or 1 year above got promoted to the group. He hated that 4th day and thought it was a bit of a waste. Was even yelling at them to give better service even though these girls were supposedly "elite" keepers playing at the highest level. Should we at the teen years ban even elite girl goalkeepers from elite goalkeeping camps even though by age 14 they can't even compete with flight 2 male goalkeepers (one of which was in the group and was actually stronger than all the remaining girls who outranked him) or is it about training and participation there? I note there are several goalkeeper coaches around town which do not at the teen years mix the girls in with the boys for this very reason, and I note there are even a few which discouraged girls from even attending elite session no matter their rank or age.
Find a mirror. Look at your neck. It is thinner than a man's neck.
You don't put girls as keeper in a U17 boy's game because they would break bones.
That is true, even if the broken bones belong to someone who really, truly believes they are a boy. Gender identity doesn't override physics.