This is a question I have tried to discuss on various forums over the years but very often people begin to feel defensive because where ever "difference" is involved, many folk try to turn difference into "better-than/worse-than".
If one accepts that gender is "a scale" (from masculine at one end to feminine at the other), there can also be another factor in "strength of expression". On that hypothesis, the average (non-trans) person would tend toward one end or the other and have a moderately strong expression. By the same token, one could be quite feminine (for example) with a weak expression and live comfortably androgynously.
Now if one assumes that "gender" on that scale is not necessarily fixed but may shift due to various factors throughout life, then everything we see makes sense.
Personally, as a child, I fell toward the feminine end with a fairly strong expression so it was apparent to most adults that "This kids isn't normal" but growing up in the 1950's the only "not-normal" that anyone knew about was homosexual - but I didn't fit there either.
Because of my gender and strength of expression, I HAD to fight to find the means of expressing myself. Despite the lack of resources (small village in the middle of a backwards area) and general ignorance, I HAD to ferret out information, find resources, and educate doctors in order to get help. (I also had to walk a fine line because if I pushed too hard, I would have been committed to an institution for being "delusional"!) Up until about 1967, I was the first 'transsexual' that most doctors had ever seen. (Dr. Benjamin's book, 1966, and being 'pronounced' by Dr. Benjamin that same year was the first credibility extended by the medical profession!) I simply could NOT pass for a boy in childhood and adjusting to male life was out of the question. The situation became even more acute after puberty.
Now I was not a frills-and-lace type of girl - more the horses and jeans type but with hormone therapy (1968) and SRS (1974) I noticed my drift toward ever more feminine in my basic gender as well as an increase in strength of expression.
In observing the trans community for the past decade, it would seem that the "gender scale" and "strength of expression" would explain the wide variation in "paths" and "time-lines ". Adding the idea of "gender drift" expands the envelope even more.
Hopefully no one will turn this into a better-than/worse-than debate. I really don't see it as any different from diabetes - some are struck early and severely and others "drift into it" through a lifetime.