i didn't start hrt until well into my adulthood and well after i figured out i'm trans, and it was one of the best feelings i've had and the mental changes were almost immediate. after starting i did have a couple weeks of what i guess i'd call "brain fog" (which i'd get each time i'd up my dose :/ ), but after that i really felt at home in my body for the first time.

i had pretty severe problems with dissociation prior to starting hrt that are pretty much gone, and every feeling is much more vibrant and feels much more like Me. it's not something that eliminated my anxiety or depression, but it did make them addressable for the first time, and even feeling Bad in a body that feels like my own is preferable (at least for me) to feeling Good in a body that doesn't.

it's something i couldn't recommend more and i really hope you're able to start!