As has already been said, the worst part of transitioning a little later may be due to all the time lost.
It doesnt seem to make a difference as far as the effectiveness of the hrt in some cases, it can be just the same for a 30 something year old as a 17 year old. I barely had a puberty at all, so not much damage done by t.
All the lost time is a major bummer though. But I plan on living as a 20 something year old for the next few years and then as a 30something year old when I'm in my 40's.
It helps when you don't age and look younger, so i will make up for lost time.
My mom looked like she was about 18 when she was hitting close to 40 and my dad has always looked way yonger than his age too. Lucky me that this seems to be my case as well...
This doesn't change that I wanted to transiton in my teens but couldn't. Will never get to do that now.