memoires I'm curious about your 'former times' when this behaviour would be considered debauched. My, meagre admittedly, knowledge of former times is that girls coming out was simply to catch a good marriage and if that meant she, at 16?, married a 70 year old Duke, that was perfect! Marrying a 40 year old, as long as he was of good family and posseassed a fortune was very good indeed.
It's a bit difficult to answer this because the life-course parameters were very different to today, but the average age of marriage for an upper class deb in the Victorian period was about 19. And upper class debs were the youngest to marry of all the social classes. Considering you were meant to have finished your education, be extremely accomplished, speak at least two languages, and able to run a substantial home of your own (which, in that period, meant running an operation that was somewhat like a business with at least four employees and possibly as many as 400), I reckon you could argue a corresponding age today would be about 21+.
Interestingly, the average age of marriage for a working class woman in 19th century Manchester was 27 and the overall average marriage age for women during the 19th century was 22. Indeed, during the 18th century, the average age of marriage for women was even higher at 26.
The marriage of a 16 year old to a 70 year old would have been socially frowned upon during the 19th century because it wasn't really a good match. The general perception would have been that the girl in question would soon be a widow, would be unlikely to bear children, and would never have the experience of "young marriage", which was somewhat of a growing notion in this period due to Victoria and Albert's model of youthful "love" match, and depending on whether there were sons from a former marriage, such a bride could easily find herself in very constrained circumstances in the event of widowhood.
In the 17th century, it would be somewhat different, but in the 19th? It would be frowned upon. People in society would feel very sorry for the girl and would cast judgement on her parents for allowing the match to occur.
The reality is that the average age of marriage in England from the mid 16 century to the mid 19th century hovered between 25 to 30 years old. As such, for a male at the age of 40 or above, having sex with young girls in their mid teens was an act that fell outside of the recognised norms of society, no matter where on the spectrum you were. You couldn't really do it within society, so it was something that you would pursue outside ... if you were so inclined, that meant procuring a young girl from a brothel etc, so therefore became a matter of "debauchery" and "perversion".