You still have a son.
Reality does not change no matter what mental process he has been through to declare he is no longer your son but some other person.
He is not too old to be caught up in social contagion or to succumb to the lure of an ideological cult.
Whether he grows his hair long, tries to dress like a slutty barbie & announces you have to call him the opposite sex or not, he is still & always will be your biological son.
Just as you would grieve if he was seriously mentally ill & had to be locked up for life, you have the absolute right to grieve for the loss of that bright child you could foresee a healthy future for.
It is not all about him.
The narcissistic cult of gender ideology is based on the 'all about him' model.
You have the right to feel however you feel & if that includes revulsion, grief, confusion etc.. it's all just as valid as whatever he says he feels.
You didn't do anything wrong here.
It is not your fault.
You don't have to pretend to believe him or at least call him something fake to his face.
If you don't however, you might lose him completely.
That is your choice.
Do not get rid of old photos etc.. you have to please him however.
Put them somewhere safe he cannot get them if you must, but don't join his melodramatic rewrite of his life.
He doesn't get to rewrite your life to fit his fantasy.