Seems to me this is practically a rule. And it seems to make a lot of sense to me, given that trans folk, before HRT, do not experience the puberty they had expected. I tend to reject or redefine the puberty that I did have, and in many ways have remained stuck in a lot of ways in a pre-pubescent state... I can imagine maturing into a more or less ordinary woman (and for social reasons would probably try to present myself that way even though I don't feel that way, if I had moved onward into HRT, etc. already).
FWIW, I've seen similar conversations over time, and all those I can recall have seemed remarkably similar in pointing out that, at least for those who have not begun to transition, many and maybe most tend to remain stuck in terms of how they see their age. I've been taking my kids to events with their teen and younger friends for several years now, and the remarks from other parents seem to share a common observation: that I am doing more than they would (their circle of friends tend to gather on weekends in locations usually over 100 miles from where we live) -- this winds up being a combination of admiration for my devotion to my kids, but there is a strong tinge as well of "that's really weird."
One strange thing, when I was in my pre-teens, most of my social interactions tended to be with adults (mostly teachers and other school staff); now at 53, I tend to feel more at ease with and understanding of the thinking of those in this circle of friends who are pre-pubescent (hastening to add that, for my own safety, to allay any possible suspicions, I'm very careful to stay in open, common spaces to ensure that misunderstandings don't develop, and generally, I only converse with the kids who actively approach me to ask what I'm doing on my laptop during such gatherings).
