He did not go to jail because he married the girl, and the likely age of consent at the time would have been 16. So although a 21 year old man having sexual intercourse with a 16 year old girl is questionable behavior, technically it would likely have been legal. I suppose that back in the old days this was more common. For perspective, this same man had a sister who also became pregnant by a 21 year old man, got married, and delivered a child all at the ripe age of 15. It is unsettling when you consider that Sheila Lyon was abducted just a few days shy of her 13th birthday.
Just to be clear, marrying the girl is not a legal defense. Marrying an underage girl just makes it likely that the crime will not be reported by an upset girl or her relatives.
The age of the Lyon sisters would closely match Lloyd's criminal tastes in girls, but to be fair to Lloyd, he did marry someone his own age.
If the or one Lyon sister looked older than they were or were trying to act older as many kids did to hang out with older kids, perhaps they would have caught the eye of someone into fourteen or fifteen year-old girls. This would be a disaster waiting to happen.
But it was Lloyd who was staring at the girls that day to the point of a confrontation.