many people still disapprove strongly of 19-year-olds involved with 45-year-olds

Well, for me, this is very funny because of my life experience. First, my birth mother was 15 while my birth father was close to 50. (BTW, she was punished for it, not him.) Second, my second wife was 20 when I met her. I was 48... also close to 50. Today, my second wife is married to another older fellow. The three of us are still good friends.

As for the age of consent, I object to any societal intrusion into personal lives of its members. Yes, I know the arguments that are formulating in your head. But, if I may suggest, consider the difference between malum in se versus malum prohibitum.

Me, kissing a six year old should not be prohibitum yet it is. Why? There is no malum in se involved. She likes it and I like it. She does not know to NOT like it, i.e., the ramifications of what will be perceived later on due to societal influence on what She is supposed to think. For that reason, I abstain from the kisses. It is societal interference in Her life that I fear. If there were no bad results later on, then the kisses can only be a good thing, no matter where I put those kisses on Her. She likes it and I like it.

You do well to point out the absurdity of an arbitrary "yes/no" line no matter where it's set. Yes, some 19 year olds can be too immature to handle crossing the arbitrary line just as some 15 year olds can be mature enough to do so.

Nevertheless, having any kind of societal intrusion into the private lives of its membership for exclusive malum prohibitum reasons is still wrong. In fact, all malum prohibitum dictates are wrong if that is the sole reason for its existence. Determining the practical difference between both concepts... well, as the Bard would say, there's the rub.