This is such a ridiculous argument.
Per this article, if that is the case, then people should be treated as children until the age of 25 - men and women. Alternatively, 18 years of age is a reasonable point at which to allow people to take responsibility for their own lives.
Therefore, I absolutely could not care less if an 18 year old dates a 90 year old, or any variation in between, as long as it is consenting. It is none of my damn business.
I know several people in successful, long term age gap relationships (including my brother) and I have precisely zero tolerance for this kind of puritanical, judgemental bullshit.