As time permitted, I've been adding dates of birth and death to my Pyramid celebrity roster. Here are a few things I got just from briefly reviewing:
The celebrity born closest to my own birthday (11/29/63) is Allan Kayser, from Mama's Family (12/18/63).
By DOB, the first celebs who weren't born when Pyramid debuted are Neal Patrick Harris and Greg Vaughan, both 6/15/73.
The first show to feature a celeb younger than the Pyramid format was the 9/19/02 show, featuring Aries Spears.
Kelly Packard (9/19/02) was the first who wasn't born when The $25,000 Pyramid debuted (1/29/75).
Eric Winter (5/12/03) was the first who was born after the switch from $10K to $20K. (However, it's possible that Marion Jones was born after the first 20K was taped.)
Kyle Lowder (5/13/03) was the first who was born after the 20K left the air (8/27/80)
Kristin Holt (2/10/03) was the first who was born after the final NY show (8/17/81).
They never reached a point where a celebrity was born after the first CBS 25K. If CBS picks it up again, that will be something to look for.
I didn't include celebs whose only appearance was for charity. It wasn't clear where Miss America Week from 2003 fits in, but either Erika Harold or Katie Harman could have filled a gap in 1980, as IMDb gives 1980 as the birth year for both, but doesn't have the day for either.