If I remember right the mid life crisis started after Sophia gave birth to Dylan(no comment from me here) so he could of been of a youngish age to notice this,if it ever happened.
Sophia also mentioned she got pregnant with Ellie after college and got married just after graduation. I don't remember in which point in the game she mentioned this.
So, it makes perfect sense that Sophia is 38. Ellie is 19 (probably), Sophia and Liam has been married for 18 years. She is right at the start of her middle life crises.
Also, for the fact that Sophia is a lot more lusty after just few weeks without sex. Man normally loses their libido when they age while woman's libido normally rises with age. She is in the phase of her life when she is most... 'needy' let us say.
EDIT. I could probably get a link of some research explaining this, but i'm a lazy fuck. Sorry.