Age gap relationships are problematic with a high rate of abuse and power dynamics. However if a man (over the age of 25) are targeting women (ages 18 to 24) this issue becomes compounded due to the brain development factors. Anyone who dates with this power dynamic are basically grooming the underdeveloped. The difference between a 21 year old and a 28 year old is enormous. As a society, we have to make laws to protect those who don't understand the consequences of their actions, much like their teenage counterparts.

Here is the study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3621648/