I'm sorry, Count, but Joker looks about mid 20's in TKJ origin:
Same in the aforementioned Batman Confidential one:
A couple of creases on his face when he smiles doesn't make him look wrinkly lol. Even Batman's face creases up when he smiles:
It's not a sign of old age. Some people's facial skin just crease when they smile;
His face is hardly "wrinkled":
I wouldn't call Joker's facial expression in B'89 when the gargoyle is dragging him down the ladder a look of disbelief and acceptance. He looks scared, IMO:
You're right we never saw Romero out of make up, and that may be why it hid his age. He was covered in make up, and wore a green wig. He wouldn't be the first actor to have their age masked by make up.
When people say Jack was playing himself as the Joker they mean it's the same crazy Jack style of acting. Obviously all the characters are different, but the same manic Jack acting style is there in all his performances.