There's no way Quinn is in her thirties.
Quinn said Mary was one year younger than she was, although the actress was 7 years younger than Constance Zimmer, who looks a good bit older than her listed age. I think Quinn was just lying about being close to Mary's age.
Zimmer is listed as 45 (although in close-ups, I think she looks closer to 55, perhaps smoking, too much sun, and no touch-up work done).
Quinn has to be at least Zimmer's age, because she got the call from the doctor in the episode before the finale, confirming she missed her chance to have children. I'm assuming, what with her affairs with Chet and Henry, that she'd been on the pill, and like some busy women, take it all the time to avoid the nuisance of menstruating, and didn't notice she was entering menopause.
Some women also reach menopause early. While it's usually about 50 or after, some women can reach it in their 40s.
Mid 40s would not be unusual, but I was responding to a post that said she was in her mid to late 30s.