On Clair's birthday, Cliff & their kids surprise her with an act.On Clair's birthday, Cliff & their kids surprise her with an act.On Clair's birthday, Cliff & their kids surprise her with an act.
At this point, the Huxtable's celebrate Claire's forty-sixth birthday and repeatedly tell her how good she looks for her age during the episode. However, that's because she was only 40 when the show aired.
In season 1.6, Cliff admits he chose Hillman Collage to follow Clair. In season 3.20 Cliff turns 50. In season 5.21 Clair turns 46. Doing the math, when Cliff was 18 and choosing a collage, Clair was roughly 12 years old.