I laughed when I read this - and then I stopped to think for a minute and couldn't really find any rational reason to deny his claim in a world where we are supposed to believe that 'transwomen are women'.
TRAs say that biology is meaningless, a person might have XY chromosomes and a penis and testicles and male hormone levels but if they wish to identify as female we need to respect and accept that, regardless. I wish some TRA could explain to me what the difference is between that and this man wanting to identify as being 20 years younger.
'But he was born in a specific year' - yes, but he feels 20 years younger.
'He is chronologically a specific age' - what is age? Do any of us really know how truly old we are?
'The telomeres in his cells denote age and his bones will also show his age as well as his teeth' - some people have younger telomeres than their calendar age would suggest. Some people look younger than they really are. Can we trust telomeres? If he can get work done to his teeth and plastic surgery on his face, then who's to say that he is not in fact 49 years old?
'We all have birth dates on our passports and ID cards, we can't just change that willy-nilly' - people have been changing their age for millennia. It's always been there as part of human culture, it just hasn't been officially accepted before. Generations ago our concept of age was much more fluid anyway, some people didn't even know their formal birth date. We need to move on from this teleological cis-age narrative and accept that we are only as old as we feel.
The satire writes itself...