I started hormones a couple months before my 29th birthday. There was no way on this earth I would've ever passed before HRT. I'm now 10 months on HRT and I decided to transition 2 months ago because the hormones changed my appearance so much, that I had to convince people I was male if I was presenting as a male. My appearance continues to change rapidly. So I would have to say that it is entirely possible for hormones to have a strong effect while you are in your 30s.
I think it has more to do with your bodies susceptibility to estrogen, along with the amount of damage that testosterone has done to your body, especially during puberty. I had a very mild puberty (low sex drive, little bone changes in the face, little growth in hands and height etc), and I think that's why HRT has been very effective for me.