Some thoughts: If you need to, write down what you want to say, hand it to the psychologist, and don't say anything - let them just read it. Put something in there about this being scary as you-know-what, but really important.
I am 40. I just started (Sept 2017 for hormones). I can still easily (sadly) pass for a guy on the hormones, but YMMV. I definitely have breast growth, but small and, if I had the desire, easily disguisable still.
For me, I knew this was right a few days into HRT. My mind is right, my emotions are mine now, and I have more energy than I ever have in life.
You can see my avatar - that's no photo magic (it would be a lousy advertisement for a photo editor if it was!). I don't look like a football player or marine, but I'm also far from blending! I get sir'ed a lot, but I'm me. I'm full-time everywhere but work now, and will be full time at work in two weeks. I mean my other option is to be a boy the second half of my life. Ick. I'd rather be a non-blending woman than a man the rest of my life.
Besides, this is the most masculine I'll look the rest of my life - the hormones will continue to do their (painfully slow!) thing and it'll get better. But even if it doesn't, I don't regret what I am doing.
I've seen other ladies our age and even older that could be models if they wanted - very conventionally beautiful despite a late transition. We're all different.
My advice: Definitely tell whoever you're seeing for therapy. And look at, "What bothers me the most?" For me, it's facial hair, and if that's the case for you, start hair removal as soon as you can. You don't need hormones or anyone's permission to start that. Also, if you can find a local support group, I find that fantastic - among other things, it's a safe place (relatively) to dress and be yourself, which I definitely needed. They'll also have good local resources.