That is simply not true. Jesus died, for heaven's sake. She did too. She did not have original sin, but she was till human. Do you think she never got gray hair or arthritis?
I do not think Our Lady grew old or ever got sick, so no, she did not have gray hair or arthritis. She was not subject to the effects of original sin. She was not a normal person. She was special. She was perfect. Just as she was spared from the pains of childbirth, another effect of original sin, she was spared from all earthly sickness.
As for what she looked like, I think she looked like Our Lady of Guadalupe.
You don't need to be an immaculate conception to have no gray hair no arthritis. There are cases of very beautiful, strong and healthy old people. It is rare but not impossible.
Also, women who have very very little child brith do exist.