Your questions are asked frequently, unfortunately there is no firm answer so I have to talk in generalities.
Generally, hormones do very little, but they change so many things just a little bit, that it may become noticeable.
Breast growth may be your biggest tell, then, eventually fat migration and muscle atrophy. So much of being female is an act. Makeup is an act. Hair is an act. Posture is an act. Clothing is an act. Voice is an act.
If you avoid these things, people will likely see you as you present, which would be male.
I tend to present very androgynously. When I do, I am typically gendered male. I currently reside in a place with almost zero trans rights so I do this for self protection. I prefer presenting female. But the hormones, and keeping my alcohol intake to a minimum quell my dysphoria and allow me to survive this way. That and coming out to everyone who is close to me.
I have stopped trying to me ultra masculine. It is funny, transition has made me secure in my masculinity so I no longer feel the need to force it. I just am who I am. People like me more. But I do long for a day when I feel right about going full time. Also my boobs are impossible to hide. Hehehe. People see moobs if you act like a guy. They aren't. They are boobs.
Hormones are no joke and you will change in unexpected ways. If they are working for you, you will know it quickly. Probably within a couple of months you will be sure. In that new mindset, don't be surprised if you just want to go full time, or any number of other unexpected turns. It is a wild ride and many of the physical changes will be permanent.
I hope you also have friends/family you can talk to about this. It helps.
Anyway, welcome to Susan's. We are here for you. Keep us posted.
P.S. I am 39 and started at 37. You are fine age wise.