Actually, Eliza, the age of 13 was set by English Law in the 1875, and only raised to 16 in 1885. That it was very much in recognition of the social mores of the day, which the folk world recognises. As I commented on another thread recently, child abuse had been a theme of social reform for some time, I quoted Nancy from Dickens' Oliver Twist as an example from 1837. Far from the wholesome mother figure in her early 20s of Oliver!, she's just 17 at the time, yet has been the mistress of Bill Sykes for a good Oliver's age, and he's 10: so that was when she was 5. And since then she's thieved 12 years. She's seventeen, or younger.
The age of marriageable consent in feudal days was puberty, for two reasons: political and survival of the species. The political was stabilising, as knowing which families intended dynastic liaison from early on removed sexual contention as one source of Court friction. The survival aspect was more important: life expectancy of boys was not what it might be at that level, with things like the Crusades sucking them in. However, we have a more stable society, and that argument no longer should be prevalent.
The question of feasibility will always have children experimenting, and the recent cases of relationships between young people aged just months apart, but one over and one under the age of consent, being punished with the full weight of the law because that is what the law requires is evidently unjust. The law is there to stop minors being abused by adults far older than them, far more experienced and therefore manipulative. It was written because of child prostitution, and worse: it was also only at that time that the law on murder was extended to children.
Another documentary cause is to be found in Fanny Hill. Written at the end of 1748, it tells of the corruption of a young girl who falls on hard times aged 15. Had the age of consent in moral terms been considered less than that, there might have been little cause for concern, but as it was, it was banned until the 1970s.
Personally, I am worried about this whittling away of childhood. It may be preferable to identify what is causing the decrease in the age of puberty, and therefore the hormonal urges which follow, than to simply follow mindlessly. Sex produces babies, as no prophylaxis is 100% effective, and a girl's body must be physiologically strong enough to do so safely. That, I consider, must be the governing factor, and the Law must protect the weakest. 16 has worked for many years, and there seems no good reason other than licence to change it.