By visualizing Mun in this Youtube Gameplay uploaded by Kanzalone, Mun appears as a young teenager, probably around the age of 15. This age appearance might seem strange, considering that Mun is part of a particular space mission crew, making her a bit too young for her profession.
There is yet to be any official height for Mun. In this Youtube Gameplay uploaded by Kanzalone, when we do a scaling observation of Mun relative to her environment, Mun appears to be fairly short. This gives us a conclusion that Mun is probably somewhere around the height of 5 feet.