The page says: "John's birthday was just before they had come to the Lake; Susan's is New Year's Day." (Where is the source for Susan's birthday?)
This gives a possible clue about the relative ages of John and Susan. If John was born in early/mid July, this is just less than 6 months before New Years Day; it is unlikely that Susan is less than 6 months younger than John. A year and a half seems like a reasonable age gap, while I think two and a half years is probably too much. If John was born in July 1918 and is 12 in July 1930, Susan being a year and a half younger would mean that she was born Jan. 1, 1920, and is 10-and-a-half in July 1930. (Are these ages plausible, or is it more likely that they are a year older: 13 and 11-and-a-half?) 99.30.130.169 23:43, September 9, 2010 (UTC)