You should be getting kids when you can provide a stable home for them, and that includes a reliable source of income and a certain level of maturity. This is usually possible in the late 20s. Waiting a couple of years beyond that is fine, but it starts to become inadvisable at 40-50. Not only because you risk unhealthy children, but because there's a fairly big chance you won't be along to see them grow older than 20-30.
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