I've had conversations like that with trans girls who transition in their teenage years.
I've been told, to my face, that "You do realize you have [insert something that happens from androgenic puberty] 1, right?"
Put the keyboard down and touch grass. That is Internet Brain Poison spawned from the depths for 4chan and TTTT.
The reality is transition does one thing before it causes physical changes: It starts the mental changes. I've joked that estrogen is the only antidepressant that has ever worked for me, but it's also true. Transitioning will change how you see yourself - and that is worth more than...whatever minor details your dysphoria fixate on? That may or may not change, but after a while you might find you don't care anymore because you're happy.
I transition at 34, and I'm beautiful. I may not be conventionally attractive by societies standards, but fuck that, I'm fucking gorgeous and I'm happier than I've ever been in my life.
It's only too late to transition once you hit the morgue. Before that, the best time to transition is when you're ready.
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This post originally had examples of the changes that people talk about or the minor details dysphoria fixates on, but I didn't want to trigger anyone's insecurities by being specific.