MILF is 20-45
Over 45 would be "mature" (euphemism) or just "granny"
that'd be wrong.
a milf (besides being an actual mother) is 38 at minimum and 60-ish at most. there are plenty of women who don't look a day older than 50, despite being over 60. but below 40 is more like 'young mother', or just "mom" territory, rather than milf.
the whole 'thing' about milfs is that they're supposed to be old enough to be the mom of your friend, who is the same age as you. it was originally about lusting for a friends mom.
to me a milf is specifically an obviously mature woman, obviously older than me, with a very curvy body, huge ass and big tits. can even be a bit chubby. in fact, preferably is. but most importantly, it's the personality that makes a milf, but the physical aspects have to be there first.
if gianna michaels, as she is today, had an even bigger ass, she'd be near-perfect example of a perfect milf. and she's 42 by the way.
so age is definitely not the best criterion for what makes a milf. it's one of the least important. but it would feel really weird to call a woman that is younger than me a 'milf'. calling a 25 year old a milf is just absurd at any measure. that's just a mom.
"mature" is typically a post-menopause woman.
"granny" is typically a graying, or otherwise very obviously old woman, who likely has, or could have grandchildren.