Considering Jeffersons time period in history I see very little relevance to an older man and girl conceiving unless it was forbidden by law. As contradictory or famous his life the article does not raise the question of his act being lawless but rather a comparison to today’s standards and laws.
Go back a couple thousand years and we see the virgin Mary, a child in her own right being conceived by God. Does this make God a sex offender? Or a child giving birth an acceptable standard in the society of that day?