technically, Rachel Starr wasn't a MILF by the time this thread had been started, but now that she is 30 that's different...
In my modest opinion, a MILF have to fill some conditions to deserve the title :
- be a ****** : unknow for rachel so that's a
"NO"
- be over 30 & below 50 : since a few months that's a
"YES" 
- have big and fake boobs : they are fake but not so big, should be at least E/F cup to satisfy the condition, so that's a
"HALFWAY"
of course we all have seen milfs "who are not a ******", milfs "aged only 22", or milfs "with a flat chest" but these requirments of part of collective mind.
despite all these considerations, her overall look is definately "MILF", she doesn't look like being the average 18 pornstar since years.
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I don't know how she looked back in 2012, but it must not have been so different...