Living, non-dividing cells (such as oocytes) can still gather damage to their DNA through a variety of ways (mutagenic substances, radiation, etc.). Misrepair of DNA damage by the cells' own repair mechanisms can form mutations which can be inherited, if the mutations don't make the oocyte non-viable of course.

The most common ways of DNA changing is methylation of Cytosine in the DNA. It’s not damage but it blocks translation from happening at that spot and the spots local to it. It effectively changes the expression of that area of DNA.

They were there when you were born, but they could have mutated before your birth. There is a long line of cells between the fertilized single cell embryo that become you, until your oocytes were formed. Any of those cells along that line that develops a mutation may pass it on to their daughter cells until eventually the oocytes were formed, inheriting the mutation.

The egg they produce may well carry that mutation and then to your child.