// Sex is determined at conception and recognised at birth or perhaps earlier of a scan is taken.//
Note that such scans determine sex *visually*, and rarely -- if ever -- by checking chromosomes. It's true that in the vast majority of cases they're likely to correspond, but there are equally rather a lot of exceptions: these are "intersex" people. As an example, Caster Semenya is intersex, as she was assigned female at birth but turns out to have XY chromosomes.
Depending on how you count, there are as many as 1 in every 270 people who would count as intersex, or around 30 million worldwide. The "depending on how you count" here is doing a bit of work, as other estimates come out lower, but a lot is to do with what even counts as "intersex", and I'm choosing here to go with an upper estimate that covers most conditions differing from the "usual" genome (ie XX = female and XY = male) (see
https://onlinelibrary.wiley.com/doi/abs/10.1002/ajhb.10122 ). Note, too, that even in sources giving lower figures, a distinction is drawn between "chromosomal sex" (ie, whether a person is XX or XY) and "phenotypic sex" (ie, whether a person is born with a vagina or a penis); see eg
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5866176/ (karyotype here meaning chromosomal content). No doubt the response here is to say that "well these are just rare cases", and yes they are not common, but even still if you have several million people who one way or another *don't* have the biology you'd expect then maybe it's worth taking notice of rather than just ignoring them or brushing them under the carpet. Biology is more complicated than you'd get from studing A-level biology.
Still, none of this is strictly relevant to
gender. This wrestler is a boy (well, a man now) because that's how he sees himself, that's how others see him, and so on.
As to whether the prefix "trans" is necessary... funnily enough, you've hit upon a key point of recent transgender politics. You may or may not remember the "trans women are women" slogan, which -- regardless of whether you agree or disagree, no doubt you'd say the opposite -- is precisely about arguing that the trans label shouldn't be necessary.