I'd say it depends on the woman. Some women are comfortable getting pregnant young, like me (i'm 21) some women prefer to wait til they're more mentally and financially strong.
As the posters above said, Women over 35 have an increased risk for chromosomal disorders such as Down Syndrome and other things.
There are also higher risks of things like placenta previa, as well as problems with birth and labor (older women have a harder time keeping energy up for the labor and delivery)
But as losingMyMind said, Lots of women over 35 have had healthy pregnancies. I myself happen to be one of those younger people who fell into the statistic group for Down Syndrome, my son who will be born soon has it. :)
I agree with what the poster above said. Women who are pregnant and are 35 or over are considered "advanced maternal age" and typically are considered high risk. There is a higher change of multiples when becoming pregnant over 35 and an increased risk of chromosomal abnormalities such as down syndrome of the fetus along with higher risks of other birth defects. With that said, many, many women have extremely healthy pregnancies/babies when becoming pregnant over the age of 35. It's best to get your health checked and possible consult a geneticist to determine your risk factors for genetic disorders etc.
the age of being ready for a baby depends on the individual. my husband and i married at 25 and enjoyed 5 years of just us before decided to start a family at age 30. i'm now almost to my 9th month in pregnancy and doing great! as you pass the age 30, the risk factors do go up slightly for downs syndrome and other chromosomal diseases. but zillions of women over 30 have totally healthy babies!! i just turned 31 and have a healthy baby and was blessed that it only took 3 months to conceive. they say once you reach 30, it's slightly harder to get pregnant, but i think most of the difficulty and risks are for women over 35...but again, this does not go for everyone. it's just a statistic. good luck to you and your lady :-)