It is very risky to specifically state an age for any of the Sailor Senshi on a profile page because they get older as the series progressed. It’s easier to state their birthdays and then calculate from there how old a Sailor Senshi was during a specific time or season. Here are their birthdays with year:
Moon – June 30, 1978
Mercury – September 10, 1978
Mars – April 17, 1978
Jupiter – December 5, 1978
Venus – October 22, 1978
Neptune – March 6, 1978
Uranus – January 27, 1978
Pluto – October 29, 1976
Saturn – January 6, 1981
Chibi/Mini Moon – June 30, ????
Tuxedo Mask – August 3, 1975
Star Healer – February 8, 1979
Star Maker – May 30, 1979
Star Fighter – July 30, 1979
It’s important to note that the time in the Sailor Moon world was parallel to real time when the show first aired in Japan. For example, the show aired on March 3, 1992 so in Sailor Moon’s world it was also March 3, 1992. Time in Sailor Moon’s world continued like this throughout the whole series. This is how I was able to calculate what year everyone was born in.
It will be very difficult for me to map out each character’s age during the progression of the entire season so I will map out Usagi’s (Sailor Moon) age throughout each season and hopefully, you can use the birthdays to figure out everyone else on your own.
Usagi was 13 years old when the show aired on March 3, 1992. However, she was 14 years old by Japanese Episode 17 so she was 14 years old for most of the first season. (Okay, this part gets confusing.) The only episode where we see Usagi celebrate her birthday was Japanese Episode 101 in Sailor Moon S when she wanted a pair of glass slippers that was later infected with a daimon. This episode was Usagi’s 15th birthday, even though it was June 1994 BECAUSE at the end of the first season, the Silver Crystal granted Usagi’s wish that they would all be normal teenagers again so they jumped back one year in age. So in June 1993, Usagi turned 14 AGAIN. This would make Usagi 16 years old in the beginning of Sailor Stars when Mamoru leaves for America on May 11, 1996. Mamoru would be 19-years-old at the same time, factoring in the time jump backward.
The time jump backward essentially forced Usagi, Ami, Rei, Minako, and Makoto to repeat the eighth grade. So in order for the Sailor Starlights to be in the same grade as them in Sailor Stars, the Sailor Starlights must be a year younger than Usagi and the other girls.
Though Sailor Neptune and Uranus were one grade above Usagi, they were still born in the same year. This is also due to the Silver Crystal time jump. Sailor Neptune and Uranus were in 10th grade during “Sailor Moon S” while Usagi was in 9th grade.
However, in the manga, there was no time jump so the Sailor Starlights would actually have been born in 1978 like Usagi in order to be in her grade in Sailor Stars. Sailor Neptune and Uranus can still have been born in 1978, regardless of the time jump, because school begins in March so they could have been accepted into the grade above Usagi’s though they were born in the same year.