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It is true that if you don't have a kid before 30, your chances go way down, and quickly. On the other hand if you had a child pre-30, your fertility doesn't go down as quickly, and you can probably still have kids in your 40's. The issue with women unable to get pregnant in their 30's and 40's usually only applies to first time mothers.
Also if you don't have kids, your odds for all kinds of nasty cancers just keeps going up - so you might not live long enough for those kids you adopted in your late 30's or early 40's after all - because when their in high school or just starting to send you the college bill, you'll be in your 60's unable to retire or perhaps suffering from cancer.
So have kids early, and suffer financially (studies show a permant loss to your life time earnings) and impact your careers, or preferred level of education. Or have kids late, risk not being able to have kids, increase your cancer risk, and any kids you have (natural or adopted) you have to think about the impact of your death on them, or bearing the cost of finishing high school/college and delaying your retirement. Either way sucks - that's life , so go with what ever makes you comfortable.
After all welcome to USA - where the mother is always wrong, no matter what choice she makes, when to have kids, stay at home - working mom, displine methods, private schools vs public schools, how many kids to have .......