This is one aspect about TS4 i don't like, the lack of natural infertility in female sims in their adult lives. With MCCC, i quite often see female sims get pregnant all the way to the end of those adult years and have children, often their partner is as old as the female sim is and so any children born are heavily reliant on the eldest sibling becoming a teenager at the very least before the parents kick the bucket, otherwise the entire family disappears from the game altogether.
i wished the developers added in a natural infertility point in adult female sims just before their half way point in their life stage. That way they can't just keep having more sims all the way into their elder years and allows other sims to have children of their own without the parents getting to it first.