It gets worse. You won't believe what people assume when she becomes a young woman, and you and she are out together, just the two of you in a restaurant or whatever, even if you have huge genetic likeness.
We actually play along with it sometimes, letting folk think what they think, until one or or the other of us bursts out laughing "Oh no, he's my real father" :-)

Btw, shaving off the grey hair makes you look ten years younger, and a real sugar daddy ☺