The journey of Wonder Woman—Princess Diana of Themyscira, or Paradise Island—is also a coming-of-age story, which explains why she is constantly reinvented to reflect the young woman in tune with the times that she represents. Her companions are her sisters, not daughters—a dynamic interestingly portrayed in the post-Crisis era. She left the island at twenty; by the time she was twenty-four or twenty-five, she had died and ascended as the Goddess of Truth; and by twenty-six, she had already completed much of the journey known to us from the post-Crisis continuity.
In the continuity also known as New Earth, various issues provide information that allows for the reconstruction of the age relationships among the key members of the Wonder Family.
In Wonder Woman #47, the first meeting between Diana and Donna Troy takes place. The story establishes that the two are relatively close in age, with Diana referring to her two decades of life. In the following issue, Wonder Woman (Vol. 2) #49, it is confirmed that Diana emerged while Donna was still using the mantle of Wonder Girl; just a few months later, Donna adopted the identity of Troia.
Subsequently, Wonder Woman Secret Files and Origins #1 (1997) provides a more precise detail regarding Diana: she was 20 years old when she won the Themyscira tournament and became Wonder Woman. The 1998 issue of the same title also notes that Diana had already been operating as Wonder Woman for six years, placing her at age 26. Around the same time, Titans #5 (1999) reveals that Donna Troy was 23 years old. Thus, there is a difference of approximately three years between Diana and Donna, with Diana being the older of the two.
Regarding Artemis of Bana-Mighdall, Batman/Superman/Wonder Woman: Trinity #3 (2003) depicts the Trinity's meeting during "Year One"—which corresponds to Year 0 of Diana's career in this reconstruction. Artemis reveals she is 14 years old. Although she is 14, her physique can make her appear considerably older—a point explored earlier in the miniseries in Trinity #1, where she is presented as a young woman who could easily be mistaken for someone around 18. Since Diana was 20 in Year 0, this establishes a six-year age gap between Diana and Artemis.
As for Cassie Sandsmark, Wonder Woman #105 establishes that she was 14 years old when she debuted as Wonder Girl. Meanwhile, Wonder Woman Secret Files and Origins #1 (1998) reveals that Cassie had already been active as Wonder Girl for two years, and during that period, Diana was 26 years old. Consequently, Cassie was approximately 16, while Diana was 26. This establishes a 10-year age gap between Diana and Cassie.
Additionally, Wonder Woman (Vol. 2) #47 establishes that Vanessa Kapatelis was nearly 14 years old when Diana and Donna met. Therefore, Vanessa was still 13 at that time. Given that Diana was 20 in Year 0, this places Vanessa 7 years younger than Diana.
After reading a good portion of the material, this is the information I found regarding the ages of the Wonder Women. Does anyone know of any other publication that reveals more details?