The reason why I want this law to be implemented is to protect people who are fairly young adults (take 18 years old for example) from old adults (40+ years) wanting to date or marry them. Those old adults who are like 40 years old will attempt to date people who are 18 years old, and this is legal from the law.

My issue with that is that the age gap is way too huge, so implementing half your age plus seven will protect these young people from old adults since it makes it illegal to date people who are younger than allowed. Take 18 years old with 40 years old as an example. If we do 40 / 2 + 7, then we will come out to 27 years as the minimum age, meaning that 40 years old are not allowed to date people younger than 27 years old.

So this law will prevent huge age gaps. Change my view as to why making this a law isn't a good idea.

Edit: I realized that my view was a bad idea. Thank you for saying that.