If I'm not mistaken, and I think I'm not, Liam is the most athletic and handsome of the mature male characters over 30. On the one hand it's normal, Sophia is a beautiful woman and the partner should fit the bill, but at 40 and working so many hours, Liam should have some love handles.
L&P portrayed Sophia as very innocent, didn't know about "MILF", Liam is the only man in the last 18 years and his performance is 6 minutes long.
My point is that Sophia is likely to perceive a 40 year old man as one whose peak performance is 6 minutes. The logic behind it would be: if my athletic, love-handle-less husband performs 6 minutes, a fatter one would perform less. It might be a shock to her if Andy fucked her for 30 minutes.
What I mean by that is it would explain the possible interest in younger ones (reminds her of the time when Liam was finishing and starting over )