To compute the acceptable age an otherwise inappropriately matched couple would have to be before they could date, find the difference in their age, multiply by two, and add seven to get the age the older partner would have to be.
And remember, always round up when computing the youngest age you can date, and round down for the oldest. You know, just to be on the safe side.
Christine is 25, Donald is 43. Christine thinks she might be too young for Donald, so she reverses the half-your-age-plus-seven rule (36). This is an unacceptable relationship.
Eustace is 94, Frank is 46. Eustace considers the fact that half-your-age-plus-seven (54) makes this an inappropriate relationship to engage in. She also considers that she will be 110 before her relationship with Frank will be socially acceptable. She then considers the fact that she will be dead by then. Eustace continues on with her relationship with Frank anyway.
The converse is twice (your age minus seven).
The following online calculator makes the math easy and also calculates how long until an UNacceptable relationship becomes acceptable:
Dave: Yeh man, I totally banged that Kath chick last night.
John: Are you a pedo?! She's 15!
Dave: Nah, she's 15 and a half, half-your-age-plus-seven, I'm 17, so half my age is 8.5 and plus seven is 15.5.
John: ...Doesn't change the fact that she's my sister...
How superficial is that.
Other superficial rules have fallen away over time.
- Religion: In our society today, most people approve of a romance where the participants have different religions. Right?
- Height: It's ok for the woman to be taller than the man. No?
- Race/Ethnicity: They might be different races, ethnicities, or come from vasty different cultures / nations, and that is ok, right?
- Gender: A majority even approve of same-sex relationships.
But G-d forbid that a 50 year old man should date a 31 year old woman? This is indecent?
If you really are judging other peoples romantic relationships by this "half plus seven" rule, you need to do some soul searching.
- Hey, half-your-age-plus-seven.
- Oh? So that means you would go for twice-your-age-minus-seven? So for you that would be 73.
- Actually, it's twice-the-quantity-your-age-minus-seven. So 66.
- I'm guessing you're too dense to see this algebraically. It's alright; we can take our results and work backwards. 73/2=36.5, and 36.5+7=43.5. However, 66/2=33, and 33+7=40. Got it?
- Ah, OK. So you'd go for a 66-year-old then?
- Fuck no.
In recent years it has been misapplied to mean the lowest age that would be considered "decent" for him to date.
This new interpretation of the rule is actually quite bizarre when you consider the remarkable range of maturity among adults of both sexes at all ages.