I can only speak for myself:
I first self meded with birth control at the age of 19, started "real" HRT at 20, and eventually was followed by an endo and got a real prescription
As far as hip widening, I did in fact experience quite a good amount!
When I started wearing feminin clothing, hrt, coming etc I was made to feel very anxious due to my "inferior" measurements. I cannot off the top of my head recall what they were but they were very "manly" and it made me cry. After some time on HRT however my BONE widened considerably (by 6 months in for sure!) and as time goes on and I gain weight I am also gaining significant amounts of fat there as well. My current waist measured 28 inches and my hips measure an astounding 38! I am 22 now and am really hoping for even more growth!!! wish me luck <3
ps I am far from perfect; although the bone grew noticeable for some reason my left hip is more wide/curvier than the right, and that 38 inch measurement was 36 until I gained about 13 pounds (the post op vegetate, relax, and eat stage is what I blame it on aha!)
Also, my whole pelvis its self is somewhat "boy-ish." It would be hard for me to explain it without a visual, but woman pelvises tend to be wider and shorter, although mine is *almost* in line with an equivalent cis girls width it is definitely "taller" so sometimes when I am wearing something tight fitting I get a mini hit of dysphoria and dysphoric thought such as "omg I should have done this sooner" etc. Of course I am the only one who notices these things!

TL;DR : Hip widening CAN occur, but to increase the likelyhood of such a thing get on HRT ASAP and hope you are still young!!!