Absurdly Youthful Mother
is not about a parent that looks younger
than they are. It is about a parent who is younger
than one would expected given the have of their son or daughter.
That could be either because they had a child when they were in the very first years of childbearing age, or because the offspring is in fact not their own but is adopted, step child, etc.
So no, there really is not enough overlap to suggest that it already covers the proposed trope of a parent that looks young enough to get mistaken for their kids's sibling, regardless of their actual age.