Fertility is a word that means the ability to have a baby. Your age, especially if you're a female, can affect your fertility. As you get older, especially after your late 30s, it can be harder to get pregnant. This is because as we age, the eggs in our bodies (the cells that can become a baby) get fewer and less healthy. So if you are a woman and you want to have a baby, it may be good to have one earlier in your life.