I do not have the statistics. I would predict that in the UK percentage of late transitions (over 30) is by now significantly less than in the US. I would like to check this preciction – wonder who would have this data.
Late transitioners are typical targets of radfem derision – especially because sometimes, unfortunately, wives are involved. They are also slammed as “autogynephiles” and what not.
But I would theorize that the main reason for prevalence of late transition is the price of access to treatment. People in their late teens and early twenties – the optimal transition age – would not be able to afford treatment. And therefore they try to adjust to their birth role, which among other things can include marriage.
The NHS covers treatment since 1999. Information needed time to diffuse. But right now, a generation grew up that was teenagers in 1999-2005 – and I would suspect that among transsexuals in that generation a larger percentage has already transitioned.