Earlier is always better but 25 is good. Especially if you are not having had much hair loss or therelike. I did hrt at 23. It worked fine, for me it was about time as I noticed some stuff that I did not want to cotinue, like hair loss. I think possibly I prevented also more body hair which for me was very few at that time and now has a totally female pattern. Sadly no changes in skeleton, amount of facial hair or voice pitch at that time anymore

- thats only for the teenage transitoners.
So I think 25 is good - considering al the older ones who do good as well. And so many changes are so amazing really. A very very small note of caution though - hormones dont change skeleton at that age, that means with aging you might age a bit different than other women. On the upside normally by having HRT all the time, many transpeople look younger