I'm pretty sure that starting at any age beyond early twenties is something of a lottery. The damage is done by that point. But lots of the problems with late-start HRT are expectations-based. I know the best I'll ever achieve at my age (40s) is looking like a forty year old girl. I'll never possibly look like a cute twenty five year old girl. HRT also can't overcome factors such as genetics, age, build, looks, body type, health issues etc. And of course, luck plays a role too. Blaming any one factor misses the complexity of the process.
There are plenty of late starters here who have had phenomenal results, and plenty of younger girls who struggle. Age is far less important than we think, and I worry that blaming poor results on age alone will serve no purpose other than to unreasonably discourage transition and will lead to unhappy lives, rather than encouraging people to live the lives they want to.