he idea of a MILF who is under 30 would piss off a lot of girls I know...Heck they may be 44 and look 24 because they take very good care of themselves but would never agree to the MILF title. It would insult them maybe because around here (Washington, DC) and in other over indulgent image focused spots, MILF pretty much means someone as a minimum over 30 or 35....... 40+ is might be ore like it..lol..  
Interesting view that Las Vegas' one true legitimate (non Asian) agency has on the issue. Good for them

I hear this debate all the time.
But 100% Proof is correct..  the term MILF was originally coined in newsgroups, and first heard in mainstream in the film American Pie.  But it was most made famous by the website MILF HUNTER starring Shawn Rees. It was one of the original "reality" porn websites from Reality Kings (dont Ask productions).
The early  videos involved a guy driving down the street looking for ladies pushing prams/ baby strollers whom he would "convince" to do a porno with him.

mostly the women were young "mothers", many wom werent even actually mothers at all but semi pro porn starts looking for a break into the online arena.  

So as far as porn was concerned - it was never about age of the MILF.. she just had to be a mom (or at least pretend to be one). Thats what MILF means to me - someone who actually is a mom.

But now many people say its an age group. .. terms for age groups have changed a lot in the past 10 years but heres where it seems to be at (there are no hard rules):

18-20 TEEN (though this term itself is banned by some websites because of its connontation). Teen can also extend up to 25 if a girl still looks under 20.
20 -25 Co-ed ... im not even sure if this term is still around outside of porn casting.  It was popular a while back.
25-35(40) MILF
35/40 + Cougar  
55/60+ GILF  

Im not a fan of using Age to define what a lady is or isnt. and here's why:
I just turned 36 in March.  
Since the age of consent in basically all countries is age 18.. its appropriate to say  18 is the age at which society deems it acceptble for women to have babies. Double 18 is 36!!!  does that mean I am now officially GILF simply because I'm legally old enough to be a grandmother? (my mother became a grandmother at 40) If we dont use GILF to define a woman over 36 why would we use MILF to define a woman of any said age bracket?  .. theres a flaw in this reasoning.

I'd say... your age plus 20 years and that assumes you're a kid. Otherwise we're just "older" women. A woman 40 years old is old enough to be a grandmother, but you're not a "granny" unless you look like a granny.

A judge ruling on porn once said.
I may not know how toovdefine porn but I know it wheh I see it.

I know an milf or gilf when i see one.
If a lady has her aarp card or collecting social security she is gilf.  Until then milf

Not sure if it is true but i have heard milf is very near the top in most searched terms on the internet.

Before the internet we would havevto relyvon the yellow pages among other for escorts..
almost every city had a listing under escorts fo "bored housewives"  they were always great

C'mon folks -- there's no way we define some of the dynamite looking 18-25 year-olds in this wonderful hobby of ours as MILFs just because they have had children.  I've seen two late-20-somethings in the last year, both of whom have had two children, that I would take for college students if I saw them at the mall.  

Same logic goes the other way.  I have seen two 35-40 year olds who claim to have no children (and don't show any "classic" outward signs) who would immediately ping my dirty little mind into serious MILF fantasies.

Last thought -- there's a 41-year-old in Arizona that has the most fantastic body I've ever seen in person, great skin, no children (she says) and has taken great care of herself.  If we ran a video and pics of her, then took a survey, I wonder what the TER world would say -- coed or MILF? (Or GILF for those of you adding 20 years to some other number?)

So, unfortunately, it's not a science, but a feeling and YMMV.  Great question, Kim -- fun start to a Saturday morning.