If the white of an egg (or Albumen as it is correctly known) is watery, it is harder for a shell to be built correctly around it and can cause an egg shell to be wrinkled or have ripples on it.
As hens get older, the whites in their eggs will get thinner but some diseases such as the viral disease Infectious Bronchitis can also affect the ability of the bird to produce thick albumen (white) and cause wrinkled egg shells, even years after infection.
If a hen has a good diet of a good quality layers feed, doesn't have any obvious health problems and has access to grit, there isn't anything that can be done about wrinkled shells. Eggs can still be eaten as normal, providing the egg shell doesn't have any cracks in it. Broken eggs should be discarded as bacteria will have entered the egg (I don't waste these though, they are fed to the dog).