Carol is Lois' younger sister as established in Emission Impossible. A family photograph shown in The Fat Guy Strangler shows both Lois and Carol as toddlers with 2 years or less age difference. Lois and Peter are both 18 in Meet the Quagmires, although this is slightly skewed that Lois is two years younger than Peter in At the Hop. Peter being 18 in 1984 in Meet the Quagmires is backed up in that he won 'Most Ticks 1965' as a baby in He's Too Sexy For His Fat. This would put both him and Lois around age 43-44. Meaning Carol is roughly 40-42.