Not to defend his unbrotherlyness, but if John were 7 at the time of his fathers second marriage, he would have to be at least 10 years older than Marianne - one year to have Elinor, two more to have Marrianne. By the time he had gone away to school, she couldn't have been very old, perhaps only 6 or 7 herself - thus a possible support of Marianne's seven year reference.