The bottom answer was "correct" at the time of the trailer, however, it is not necessarily the true answer now.
The true answer would appear to be because she was given Kree blood and her powers come from the Space Stone. Kree blood is said to have regenerative powers so this could have helped her not age.
Another noteworthy trait is their highly potent regenerative capabilities. Their healing factor is considered to be so profound that S.H.I.E.L.D. attempted to use the G.H.'s blood to perform transfusions with mortally wounded, dying, or dead humans in order to resurrect them or cure them of terminal illnesses.
Marvel Cinematic Universe Wiki, Kree
Carol also receives her powers from the Space Stone and so it is likely that the power of the Space Stone is what is stopping her from ageing.
Because she is part Kree
This is stated in the second official trailer.
Fury: And you're a Kree? A race of noble warriors?
Carol: Heroes. Noble warrior heroes.
The Kree Supreme Intelligence later says the following:
We made you one of us. So you could live longer, stronger, superior. You were reborn.