Fertile octogenarian

The fertile octogenarian and the unborn widow are two legal fictions from the law of real property (and trusts) that can be used either to invoke the rule against perpetuities to make an interest in property void or, alternatively and much more frequently, to demonstrate the seemingly bizarre results that can occur as a result of the rule. The rule itself, simply stated, makes a future interest in property void if it can be logically proven that there is some possibility of the interest not vesting or failing within 21 years after the end of a life in being at the time the interest is created.

The fertile octogenarian is a fictitious character that comes up when applying the rule against perpetuities. The rule presumes that anyone, even an octogenarian (i.e., someone between 80 and 90 years of age) can parent a child, regardless of sex or health. For instance, suppose that a will devises a piece of land known as Blackacre "to A for her life, and then to the first of A's children to reach 25 years of age." A is, at the time the will is probated, an 85-year-old woman. In applying the rule against perpetuities, an imaginative lawyer will argue (and a court must accept under the common law rule itself) that A could have a child in her 86th year and then in her 87th year all of A's other children could die, then in her 88th year A herself could die. Because the interest will not vest until her new child reaches 25 years of age, which cannot happen until more than 21 years after A and her other children (together who form the "lives in being" to which the rule refers) have all died, the rule against perpetuities makes the entire gift "to the first of A's children to reach 25 years of age" void. A will hold Blackacre for life, and then the property will revert to the person whose will transferred it to A in the first place. (Actually, it will go to that person's estate, since the will was probated only after his death.)

While it is true that there is often no statutory maximum age limit to perform an adoption, and adopted children are often treated the same as natural children, so an 86-year-old woman who adopts a newborn child is legally in the same position as an 86-year-old woman who gives birth, the fertile octogenarian rule predates the laws allowing legal adoption.

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Wikipedia