Given that porn can’t sexualize anyone under 18, she would have had to be at least 18 when she conceived her first child.
Since MILFs in porn are generally “my friend’s mom” or something generationally similar, ie the MILF is defined as such by someone the age of her child, said child and their peers must be at least 18 as well.
Therefore, the minimum age for a MILF character in a porn, legally and mathematically, should be 36
If “half your age, plus seven” gets you the youngest age society will accept, then, “minus seven, times 2” should get you the oldest acceptable age.
So
(18-7)*2is 22. A mom with a 3 year-old is still a mom.And if that doesn’t suspend your disbelief, you could still slap on “step” to the relationship label and the script writes itself.