Okay, I have some questions:
1 how old was Dani Moonstar at the time of the, roughly, 2005 New X-Men series, and by extension, M-Day?
2 how old is she supposed to be now?
For the record, a part of me wants to say she was 19 when Elixir became her ward, but I'm not sure. I'm just trying to figure this out for myself.
If you take the in-universe dates and ages at face value, then we know 1) Rahne was 19 during New Mutants vol. 2/Academy X, when she worked as a teaching assistant. 2) Sam was over 21 during New Mutants vol. 3/Utopia (where he's above the California drinking age and it's not presented as a fake ID). Dani and Sam were both 16 when they were introduced, and were between 2 and 3 years older than Rahne. Utopia takes place around a year after Messiah Complex (and therefore both Academy X and M-Day), but that's also a direct reference to the real passage of time in a Marvel comic (always dangerous to trust!), so you could just as well ignore it if you want and have it take place some undisclosed number of months later. Either way Dani ends up being around 21 - 22 when she met Josh, depending on if she has an early or late birthday.
As for her current age in the comics right now... um, honestly she's probably intended to be around the same age, as absurd as that sounds? They've heavily compressed the timeline for Krakoa, so that there would be only two generations of X-Men, and part of the effect of having everyone die and get resurrected at least once is to let them just ignore age differences from here on out. If you look around at the modern comics, Laura (and her age cohort) are treated as the same age as the New Mutants or Jubilee. Xuan is dating a student and no one thinks it's weird. Illyana and Doug are presented as being in the same generation as Teen Cable, who is around the same age as the Stepford sisters and Armor. They're all somewhere nebulously in their early twenties, with the older X-Men (Scott's cohort) all somewhere nebulously around thirty.
Thanks for the question!