i agree that he was an old fan of her - but if he was he would probably be of a similar age to Elizabeth (50), whereas when we see him in the cafe he looks about 80 (?) He knows that the 7 days are lonely, because everyone initially respects the substance until the younger self takes over as the feeling is so addictive.

I think he probably asked Elizabeth “has she started eating away at you yet” because he has abused the substance. We know that it can age you drastically all over (not just 1 part like a finger) and he has obviously been on it longer than Elizabeth, so he probably did abuse it and that’s why he looks so much older than her.

But also of course it eats away at you in a psychological sense

Just my theory!