The Rugrats babies they used to relate to. Here is a breakdown of the Rugrats parent crew and their ages in the original series and the 2021 reboot.
The Rugrats adults are a quirky and diverse group. First, there is Stu and Didi Pickles, the parents of Tommy Pickles (and Dill Pickles, in the original). Stu is an eccentric inventor who frequently creates wild contraptions, while Didi has worked a variety of jobs, including a teacher, a child psychiatrist, and running an online children's boutique. There is Drew Pickles (Stu's older brother) and his workaholic wife Charlotte, the parents of Angelica Pickles. Chas Finster, who is known for being neurotic, is the father of the equally anxious Chuckie Finster. Lucy and Randy Carmichael are the parents of Susie Carmichael. Both are doctors in the reboot, but in the original, Randy worked as a writer for the Dummi Bears show instead. Last is Betty and Howie DeVille, the parents of Phil and Lil. Howie is not featured in the reboot, but Betty runs a successful cafe in the updated series.
Related: Why Rugrats Made The Right Choice Changing Betty In The Reboot
The ages of the Rugrats parents in the original have nearly all been confirmed. Didi was born in 1959, meaning she would be 32 in the first episode. This can be calculated from the year of her junior prom, 1976 (the prom was Bicentennial themed, and the US had its Bicentennial in 1976), which was mentioned in the Rugrats episode "Junior Prom". Grandpa mentions that Stu is 35 in the 1993 episode "The Legend of Satchmo," making him 33 when the series started. Drew Pickles is referred to as Stu's older brother, but the line "we were 8" in "Tommy's First Birthday" says their birthdays may make their ages overlap some, making Drew roughly 33 or 34.
Some characters' ages aren't referenced directly in the series, though they do have listed ages. Lucy and Randy Carmichael were born in 1955, making them 36 when the series began. They're also the couple with the eldest children in the series, so them being slightly older than the rest makes sense. Chas and Charlotte were born in 1957, so they were both 34 at the series' start. Howard was born in 1958 and Betty in 1959, making them 33 and 32 at the beginning of the series.
As for the Rugrats reboot, it seems the parents have kept their relative ages; their birth years have just been shifted forward to reflect the modern era of the newest episodes. The only age explicitly mentioned so far is Lou Pickle's, Stu and Drew's father. Didi mentions that Lou is in his 70s, which matches his age in the original series (Lou was 76). Therefore, it's likely that the Rugrats reboot is keeping the crew the same age.